diff --git a/examples/dqn_example.py b/examples/dqn_example.py
index 4fbe466..7d20731 100644
--- a/examples/dqn_example.py
+++ b/examples/dqn_example.py
@@ -9,8 +9,7 @@ import gym
 import sys
 sys.path.append('..')
 import tianshou.core.losses as losses
-from tianshou.data.replay import Replay
-import tianshou.data.advantage_estimation as advantage_estimation
+from tianshou.data.replay_buffer.utils import get_replay_buffer
 import tianshou.core.policy as policy
 
 
@@ -38,11 +37,10 @@ if __name__ == '__main__':
     action_dim = env.action_space.n
 
     # 1. build network with pure tf
-    observation = tf.placeholder(tf.float32, shape=(None,) + observation_dim) # network input
+    observation = tf.placeholder(tf.float32, shape=(None,) + observation_dim, name="dqn_observation") # network input
 
     with tf.variable_scope('q_net'):
         q_values = policy_net(observation, action_dim)
-        train_var_list = tf.get_collection(tf.GraphKeys.TRAINABLE_VARIABLES) # TODO: better management of TRAINABLE_VARIABLES
     with tf.variable_scope('target_net'):
         q_values_target = policy_net(observation, action_dim)
 
@@ -54,13 +52,15 @@ if __name__ == '__main__':
     target = tf.placeholder(dtype=tf.float32, shape=[None]) # target value for DQN
 
     dqn_loss = losses.dqn_loss(action, target, q_net) # TongzhengRen
-
+    global_step = tf.Variable(0, name='global_step', trainable=False)
+    train_var_list = tf.get_collection(
+        tf.GraphKeys.TRAINABLE_VARIABLES)  # TODO: better management of TRAINABLE_VARIABLES
     total_loss = dqn_loss
     optimizer = tf.train.AdamOptimizer(1e-3)
-    train_op = optimizer.minimize(total_loss, var_list=train_var_list)
-
+    train_op = optimizer.minimize(total_loss, var_list=train_var_list, global_step=tf.train.get_global_step())
     # 3. define data collection
-    training_data = Replay(env, q_net, advantage_estimation.qlearning_target(target_net)) #
+    replay_memory = get_replay_buffer('rank_based', env, q_values, q_net, target_net,
+                                      {'size': 1000, 'batch_size': 64, 'learn_start': 20})
                                                              # ShihongSong: Replay(env, q_net, advantage_estimation.qlearning_target(target_network)), use your ReplayMemory, interact as follows. Simplify your advantage_estimation.dqn to run before YongRen's DQN
     # maybe a dict to manage the elements to be collected
 
@@ -70,14 +70,16 @@ if __name__ == '__main__':
 
         minibatch_count = 0
         collection_count = 0
+        collect_freq = 100
         while True: # until some stopping criterion met...
             # collect data
-            training_data.collect() # ShihongSong
-            collection_count += 1
-            print('Collected {} times.'.format(collection_count))
+            for i in range(0, collect_freq):
+                replay_memory.collect() # ShihongSong
+                collection_count += 1
+                print('Collected {} times.'.format(collection_count))
 
             # update network
-            data = training_data.next_batch(64) # YouQiaoben, ShihongSong
+            data = replay_memory.next_batch(10) # YouQiaoben, ShihongSong
             # TODO: auto managing of the placeholders? or add this to params of data.Batch
             sess.run(train_op, feed_dict={observation: data['observations'], action: data['actions'], target: data['target']})
             minibatch_count += 1
diff --git a/tianshou/core/losses.py b/tianshou/core/losses.py
index d281df9..3461afb 100644
--- a/tianshou/core/losses.py
+++ b/tianshou/core/losses.py
@@ -32,7 +32,7 @@ def vanilla_policy_gradient(sampled_action, reward, pi, baseline="None"):
     """
     log_pi_act = pi.log_prob(sampled_action)
     vanilla_policy_gradient_loss = tf.reduce_mean(reward * log_pi_act)
-    # TODO： Different baseline methods like REINFORCE, etc.
+    # TODO: Different baseline methods like REINFORCE, etc.
     return vanilla_policy_gradient_loss
 
 def dqn_loss(sampled_action, sampled_target, q_net):
@@ -44,8 +44,8 @@ def dqn_loss(sampled_action, sampled_target, q_net):
     :param q_net: current `policy` to be optimized
     :return:
     """
-    action_num = q_net.get_values().shape()[1]
-    sampled_q = tf.reduce_sum(q_net.get_values() * tf.one_hot(sampled_action, action_num), axis=1)
+    action_num = q_net.values_tensor().get_shape()[1]
+    sampled_q = tf.reduce_sum(q_net.values_tensor() * tf.one_hot(sampled_action, action_num), axis=1)
     return tf.reduce_mean(tf.square(sampled_target - sampled_q))
 
 def deterministic_policy_gradient(sampled_state, critic):
diff --git a/tianshou/core/policy/__init__.py b/tianshou/core/policy/__init__.py
index f67b3ba..ccde775 100644
--- a/tianshou/core/policy/__init__.py
+++ b/tianshou/core/policy/__init__.py
@@ -2,4 +2,5 @@
 # -*- coding: utf-8 -*-
 
 from .base import *
-from .stochastic import *
\ No newline at end of file
+from .stochastic import *
+from .dqn import *
\ No newline at end of file
diff --git a/tianshou/core/policy/base.py b/tianshou/core/policy/base.py
index b6d8d48..eecfc4f 100644
--- a/tianshou/core/policy/base.py
+++ b/tianshou/core/policy/base.py
@@ -12,23 +12,28 @@ import tensorflow as tf
 
 __all__ = [
     'StochasticPolicy',
+    'QValuePolicy',
 ]
 
-#TODO: separate actor and critic, we should focus on it once we finish the basic module.
+# TODO: separate actor and critic, we should focus on it once we finish the basic module.
+
 
 class QValuePolicy(object):
     """
     The policy as in DQN
     """
     def __init__(self, observation_placeholder):
-        self.observation_placeholder = observation_placeholder
+        self._observation_placeholder = observation_placeholder
 
     def act(self, observation, exploration=None): # first implement no exploration
         """
         return the action (int) to be executed.
         no exploration when exploration=None.
         """
-        pass
+        self._act(observation, exploration)
+
+    def _act(self, observation, exploration = None):
+        raise NotImplementedError()
 
     def values(self, observation):
         """
@@ -36,7 +41,7 @@ class QValuePolicy(object):
         """
         pass
 
-    def values_tensor(self, observation):
+    def values_tensor(self):
         """
         returns the tensor of the values for all actions a at observation s
         """
diff --git a/tianshou/core/policy/dqn.py b/tianshou/core/policy/dqn.py
index cfc6abf..81efc9b 100644
--- a/tianshou/core/policy/dqn.py
+++ b/tianshou/core/policy/dqn.py
@@ -1,7 +1,54 @@
-
-
-from .base import QValuePolicy
+from tianshou.core.policy.base import QValuePolicy
+import tensorflow as tf
 
 
 class DQN(QValuePolicy):
-	pass
\ No newline at end of file
+    """
+    The policy as in DQN
+    """
+
+    def __init__(self, logits, observation_placeholder, dtype=None, **kwargs):
+        self._logits = tf.convert_to_tensor(logits)
+        if dtype is None:
+            dtype = tf.int32
+        self._n_categories = self._logits.get_shape()[-1].value
+
+        super(DQN, self).__init__(observation_placeholder)
+
+        net = tf.layers.conv2d(self._observation_placeholder, 16, 8, 4, 'valid', activation=tf.nn.relu)
+        net = tf.layers.conv2d(net, 32, 4, 2, 'valid', activation=tf.nn.relu)
+        net = tf.layers.flatten(net)
+        net = tf.layers.dense(net, 256, activation=tf.nn.relu, use_bias=True)
+        self._value = tf.layers.dense(net, self._n_categories)
+
+    def _act(self, observation, exploration=None):  # first implement no exploration
+        """
+        return the action (int) to be executed.
+        no exploration when exploration=None.
+        """
+        sess = tf.get_default_session()
+        sampled_action = sess.run(tf.multinomial(self.logits, num_samples=1),
+                                  feed_dict={self._observation_placeholder: observation[None]})
+        return sampled_action
+
+    @property
+    def logits(self):
+        return self._logits
+
+    @property
+    def n_categories(self):
+        return self._n_categories
+
+    def values(self, observation):
+        """
+        returns the Q(s, a) values (float) for all actions a at observation s
+        """
+        sess = tf.get_default_session()
+        value = sess.run(self._value, feed_dict={self._observation_placeholder: observation[None]})
+        return value
+
+    def values_tensor(self):
+        """
+        returns the tensor of the values for all actions a at observation s
+        """
+        return self._value
diff --git a/tianshou/data/advantage_estimation.py b/tianshou/data/advantage_estimation.py
index 6f5b8a6..3c2d644 100644
--- a/tianshou/data/advantage_estimation.py
+++ b/tianshou/data/advantage_estimation.py
@@ -19,7 +19,8 @@ def full_return(raw_data):
     returns = rewards.copy()
     episode_start_idx = 0
     for i in range(1, num_timesteps):
-        if episode_start_flags[i] or (i == num_timesteps - 1): # found the start of next episode or the end of all episodes
+        if episode_start_flags[i] or (
+                i == num_timesteps - 1):  # found the start of next episode or the end of all episodes
             if i < rewards.shape[0] - 1:
                 t = i - 1
             else:
@@ -34,4 +35,36 @@ def full_return(raw_data):
 
     data['returns'] = returns
 
-    return data
\ No newline at end of file
+    return data
+
+
+class QLearningTarget:
+    def __init__(self, policy, gamma):
+        self._policy = policy
+        self._gamma = gamma
+
+    def __call__(self, raw_data):
+        data = dict()
+        observations = list()
+        actions = list()
+        rewards = list()
+        wi = list()
+        all_data, data_wi, data_index = raw_data
+
+        for i in range(0, all_data.shape[0]):
+            current_data = all_data[i]
+            current_wi = data_wi[i]
+            current_index = data_index[i]
+            observations.append(current_data['observation'])
+            actions.append(current_data['action'])
+            next_max_qvalue = np.max(self._policy.values(current_data['observation']))
+            current_qvalue = self._policy.values(current_data['previous_observation'])[current_data['previous_action']]
+            reward = current_data['reward'] + next_max_qvalue - current_qvalue
+            rewards.append(reward)
+            wi.append(current_wi)
+
+        data['observations'] = np.array(observations)
+        data['actions'] = np.array(actions)
+        data['rewards'] = np.array(rewards)
+
+        return data
diff --git a/tianshou/data/replay_buffer/buffer.py b/tianshou/data/replay_buffer/buffer.py
index 4b92cfc..6a44170 100644
--- a/tianshou/data/replay_buffer/buffer.py
+++ b/tianshou/data/replay_buffer/buffer.py
@@ -1,39 +1,51 @@
 class ReplayBuffer(object):
-	def __init__(self, conf):
-		'''
+    def __init__(self, env, policy, qnet, target_qnet, conf):
+        """
 		Initialize a replay buffer with parameters in conf.
-		'''
-		pass
+		"""
+        pass
 
-	def add(self, data, priority):
-		'''
+    def add(self, data, priority):
+        """
 		Add a data with priority = priority to replay buffer.
-		'''
-		pass
+		"""
+        pass
 
-	def update_priority(self, indices, priorities):
-		'''
+    def collect(self):
+        """
+		Collect data from current environment and policy.
+		"""
+        pass
+
+    def next_batch(self, batch_size):
+        """
+		get batch of data from the replay buffer.
+		"""
+        pass
+
+    def update_priority(self, indices, priorities):
+        """
 		Update the data's priority whose indices = indices.
 		For proportional replay buffer, the priority is the priority.
 		For rank based replay buffer, the priorities parameter will be the delta used to update the priority.
-		'''
-		pass
+		"""
+        pass
 
-	def reset_alpha(self, alpha):
-		'''
+    def reset_alpha(self, alpha):
+        """
 		This function only works for proportional replay buffer.
 		This function resets alpha.
-		'''
-		pass
+		"""
+        pass
 
-	def sample(self, conf):
-		'''
+    def sample(self, conf):
+        """
 		Sample from replay buffer with parameters in conf.
-		'''
-		pass
+		"""
+        pass
 
-	def rebalance(self):
-		'''
+    def rebalance(self):
+        """
 		This is for rank based priority replay buffer, which is used to rebalance the sum tree of the priority queue.
-		'''
-		pass
\ No newline at end of file
+		"""
+        pass
diff --git a/tianshou/data/replay_buffer/naive.py b/tianshou/data/replay_buffer/naive.py
index 9436a39..50ba1c3 100644
--- a/tianshou/data/replay_buffer/naive.py
+++ b/tianshou/data/replay_buffer/naive.py
@@ -1,29 +1,93 @@
-from buffer import ReplayBuffer
 import numpy as np
+import tensorflow as tf
 from collections import deque
+from math import fabs
+
+from tianshou.data.replay_buffer.buffer import ReplayBuffer
+
 
 class NaiveExperience(ReplayBuffer):
-	def __init__(self, conf):
-		self.max_size = conf['size']
-		self.n_entries = 0
-		self.memory = deque(maxlen = self.max_size)
+    def __init__(self, env, policy, qnet, target_qnet, conf):
+        self.max_size = conf['size']
+        self._env = env
+        self._policy = policy
+        self._qnet = qnet
+        self._target_qnet = target_qnet
+        self._begin_act()
+        self.n_entries = 0
+        self.memory = deque(maxlen=self.max_size)
 
-	def add(self, data, priority = 0):
-		self.memory.append(data)
-		if self.n_entries < self.max_size:
-			self.n_entries += 1
+    def add(self, data, priority=0):
+        self.memory.append(data)
+        if self.n_entries < self.max_size:
+            self.n_entries += 1
 
-	def update_priority(self, indices, priorities = 0):
-		pass
+    def _begin_act(self):
+        self.observation = self._env.reset()
+        self.action = self._env.action_space.sample()
+        done = False
+        while not done:
+            if done:
+                self.observation = self._env.reset()
+                self.action = self._env.action_space.sample()
+            self.observation, _, done, _ = self._env.step(self.action)
 
-	def reset_alpha(self, alpha):
-		pass
+    def collect(self):
+        sess = tf.get_default_session()
+        current_data = dict()
+        current_data['previous_action'] = self.action
+        current_data['previous_observation'] = self.observation
+        self.action = np.argmax(sess.run(self._policy, feed_dict={"dqn_observation:0": self.observation.reshape((1,) + self.observation.shape)}))
+        self.observation, reward, done, _ = self._env.step(self.action)
+        current_data['action'] = self.action
+        current_data['observation'] = self.observation
+        current_data['reward'] = reward
+        self.add(current_data)
+        if done:
+            self._begin_act()
 
-	def sample(self, conf):
-		batch_size = conf['batch_size']
-		batch_size = min(len(self.memory), batch_size)
-		idxs = np.random.choice(len(self.memory), batch_size)
-		return [self.memory[idx] for idx in idxs], [1] * len(idxs), idxs
+    def update_priority(self, indices, priorities=0):
+        pass
 
-	def rebalance(self):
-		pass
+    def reset_alpha(self, alpha):
+        pass
+
+    def sample(self, conf):
+        batch_size = conf['batch_size']
+        batch_size = min(len(self.memory), batch_size)
+        idxs = np.random.choice(len(self.memory), batch_size)
+        return [self.memory[idx] for idx in idxs], [1] * len(idxs), idxs
+
+    def next_batch(self, batch_size):
+        data = dict()
+        observations = list()
+        actions = list()
+        rewards = list()
+        wi = list()
+        target = list()
+
+        for i in range(0, batch_size):
+            current_datas, current_wis, current_indexs = self.sample({'batch_size': 1})
+            current_data = current_datas[0]
+            current_wi = current_wis[0]
+            current_index = current_indexs[0]
+            observations.append(current_data['observation'])
+            actions.append(current_data['action'])
+            next_max_qvalue = np.max(self._target_qnet.values(current_data['observation']))
+            current_qvalue = self._qnet.values(current_data['previous_observation'])[0, current_data['previous_action']]
+            reward = current_data['reward'] + next_max_qvalue - current_qvalue
+            rewards.append(reward)
+            target.append(current_data['reward'] + next_max_qvalue)
+            self.update_priority(current_index, [fabs(reward)])
+            wi.append(current_wi)
+
+        data['observations'] = np.array(observations)
+        data['actions'] = np.array(actions)
+        data['rewards'] = np.array(rewards)
+        data['wi'] = np.array(wi)
+        data['target'] = np.array(target)
+
+        return data
+
+    def rebalance(self):
+        pass
diff --git a/tianshou/data/replay_buffer/proportional.py b/tianshou/data/replay_buffer/proportional.py
index 72d1457..63aab66 100644
--- a/tianshou/data/replay_buffer/proportional.py
+++ b/tianshou/data/replay_buffer/proportional.py
@@ -1,7 +1,10 @@
-import numpy
+import numpy as np
 import random
-import sum_tree
-from buffer import ReplayBuffer
+import tensorflow as tf
+import math
+
+from tianshou.data.replay_buffer import sum_tree
+from tianshou.data.replay_buffer.buffer import ReplayBuffer
 
 
 class PropotionalExperience(ReplayBuffer):
@@ -15,7 +18,7 @@ class PropotionalExperience(ReplayBuffer):
 
     """
     
-    def __init__(self, conf):
+    def __init__(self, env, policy, qnet, target_qnet, conf):
         """ Prioritized experience replay buffer initialization.
         
         Parameters
@@ -30,11 +33,26 @@ class PropotionalExperience(ReplayBuffer):
         """
         memory_size = conf['size']
         batch_size = conf['batch_size']
-        alpha = conf['alpha']
+        alpha = conf['alpha'] if 'alpha' in conf else 0.6
         self.tree = sum_tree.SumTree(memory_size)
         self.memory_size = memory_size
         self.batch_size = batch_size
         self.alpha = alpha
+        self._env = env
+        self._policy = policy
+        self._qnet = qnet
+        self._target_qnet = target_qnet
+        self._begin_act()
+
+    def _begin_act(self):
+        self.observation = self._env.reset()
+        self.action = self._env.action_space.sample()
+        done = False
+        while not done:
+            if done:
+                self.observation = self._env.reset()
+                self.action = self._env.action_space.sample()
+            self.observation, _, done, _ = self._env.step(self.action)
 
     def add(self, data, priority):
         """ Add new sample.
@@ -48,6 +66,12 @@ class PropotionalExperience(ReplayBuffer):
         """
         self.tree.add(data, priority**self.alpha)
 
+    def collect(self):
+        pass
+
+    def next_batch(self, batch_size):
+        pass
+
     def sample(self, conf):
         """ The method return samples randomly.
         
@@ -64,8 +88,9 @@ class PropotionalExperience(ReplayBuffer):
         indices:
             list of sample indices
             The indices indicate sample positions in a sum tree.
+            :param conf: giving beta
         """
-        beta = conf['beta']
+        beta = conf['beta'] if 'beta' in conf else 0.4
         if self.tree.filled_size() < self.batch_size:
             return None, None, None
 
@@ -91,6 +116,54 @@ class PropotionalExperience(ReplayBuffer):
         
         return out, weights, indices
 
+    def collect(self):
+        sess = tf.get_default_session()
+        current_data = dict()
+        current_data['previous_action'] = self.action
+        current_data['previous_observation'] = self.observation
+        # TODO: change the name of the feed_dict
+        self.action = np.argmax(sess.run(self._policy, feed_dict={"dqn_observation:0": self.observation.reshape((1,) + self.observation.shape)}))
+        self.observation, reward, done, _ = self._env.step(self.action)
+        current_data['action'] = self.action
+        current_data['observation'] = self.observation
+        current_data['reward'] = reward
+        priorities = np.array([self.tree.get_val(i) ** -self.alpha for i in range(self.tree.filled_size())])
+        priority = np.max(priorities) if len(priorities) > 0 else 1
+        self.add(current_data, priority)
+        if done:
+            self._begin_act()
+
+    def next_batch(self, batch_size):
+        data = dict()
+        observations = list()
+        actions = list()
+        rewards = list()
+        wi = list()
+        target = list()
+
+        for i in range(0, batch_size):
+            current_datas, current_wis, current_indexs = self.sample({'batch_size': 1})
+            current_data = current_datas[0]
+            current_wi = current_wis[0]
+            current_index = current_indexs[0]
+            observations.append(current_data['observation'])
+            actions.append(current_data['action'])
+            next_max_qvalue = np.max(self._target_qnet.values(current_data['observation']))
+            current_qvalue = self._qnet.values(current_data['previous_observation'])[0, current_data['previous_action']]
+            reward = current_data['reward'] + next_max_qvalue - current_qvalue
+            rewards.append(reward)
+            target.append(current_data['reward'] + next_max_qvalue)
+            self.update_priority([current_index], [math.fabs(reward)])
+            wi.append(current_wi)
+
+        data['observations'] = np.array(observations)
+        data['actions'] = np.array(actions)
+        data['rewards'] = np.array(rewards)
+        data['wi'] = np.array(wi)
+        data['target'] = np.array(target)
+
+        return data
+
     def update_priority(self, indices, priorities):
         """ The methods update samples's priority.
         
diff --git a/tianshou/data/replay_buffer/rank_based.py b/tianshou/data/replay_buffer/rank_based.py
index eb770af..da56763 100644
--- a/tianshou/data/replay_buffer/rank_based.py
+++ b/tianshou/data/replay_buffer/rank_based.py
@@ -8,13 +8,15 @@ import sys
 import math
 import random
 import numpy as np
+import tensorflow as tf
+
+from tianshou.data.replay_buffer.binary_heap import BinaryHeap
+from tianshou.data.replay_buffer.buffer import ReplayBuffer
 
-from binary_heap import BinaryHeap
-from buffer import ReplayBuffer
 
 class RankBasedExperience(ReplayBuffer):
 
-    def __init__(self, conf):
+    def __init__(self, env, policy, qnet, target_qnet, conf):
         self.size = conf['size']
         self.replace_flag = conf['replace_old'] if 'replace_old' in conf else True
         self.priority_size = conf['priority_size'] if 'priority_size' in conf else self.size
@@ -25,12 +27,18 @@ class RankBasedExperience(ReplayBuffer):
         self.learn_start = conf['learn_start'] if 'learn_start' in conf else 1000
         self.total_steps = conf['steps'] if 'steps' in conf else 100000
         # partition number N, split total size to N part
-        self.partition_num = conf['partition_num'] if 'partition_num' in conf else 100
+        self.partition_num = conf['partition_num'] if 'partition_num' in conf else 10
 
         self.index = 0
         self.record_size = 0
         self.isFull = False
 
+        self._env = env
+        self._policy = policy
+        self._qnet = qnet
+        self._target_qnet = target_qnet
+        self._begin_act()
+
         self._experience = {}
         self.priority_queue = BinaryHeap(self.priority_size)
         self.distributions = self.build_distributions()
@@ -98,7 +106,64 @@ class RankBasedExperience(ReplayBuffer):
             self.index += 1
             return self.index
 
-    def add(self, data, priority = 0):
+    def _begin_act(self):
+        self.observation = self._env.reset()
+        self.action = self._env.action_space.sample()
+        done = False
+        while not done:
+            if done:
+                self.observation = self._env.reset()
+                self.action = self._env.action_space.sample()
+            self.observation, _, done, _ = self._env.step(self.action)
+
+    def collect(self):
+        sess = tf.get_default_session()
+        current_data = dict()
+        current_data['previous_action'] = self.action
+        current_data['previous_observation'] = self.observation
+        self.action = np.argmax(sess.run(self._policy, feed_dict={"dqn_observation:0": self.observation.reshape((1,) + self.observation.shape)}))
+        self.observation, reward, done, _ = self._env.step(self.action)
+        current_data['action'] = self.action
+        current_data['observation'] = self.observation
+        current_data['reward'] = reward
+        self.add(current_data)
+        if done:
+            self._begin_act()
+
+    def next_batch(self, batch_size):
+        data = dict()
+        observations = list()
+        actions = list()
+        rewards = list()
+        wi = list()
+        target = list()
+
+        sess = tf.get_default_session()
+        current_datas, current_wis, current_indexs = self.sample({'global_step': sess.run(tf.train.get_global_step())})
+
+        for i in range(0, batch_size):
+            current_data = current_datas[i]
+            current_wi = current_wis[i]
+            current_index = current_indexs[i]
+            observations.append(current_data['observation'])
+            actions.append(current_data['action'])
+            next_max_qvalue = np.max(self._target_qnet.values(current_data['observation']))
+            current_qvalue = self._qnet.values(current_data['previous_observation'])[0, current_data['previous_action']]
+            reward = current_data['reward'] + next_max_qvalue - current_qvalue
+            rewards.append(reward)
+            target.append(current_data['reward'] + next_max_qvalue)
+            self.update_priority([current_index], [math.fabs(reward)])
+            wi.append(current_wi)
+
+        data['observations'] = np.array(observations)
+        data['actions'] = np.array(actions)
+        data['rewards'] = np.array(rewards)
+        data['wi'] = np.array(wi)
+        data['target'] = np.array(target)
+
+        return data
+
+    def add(self, data, priority = 1):
         """
         store experience, suggest that experience is a tuple of (s1, a, r, s2, t)
         so each experience is valid
@@ -156,16 +221,16 @@ class RankBasedExperience(ReplayBuffer):
             sys.stderr.write('Record size less than learn start! Sample failed\n')
             return False, False, False
 
-        dist_index = math.floor(self.record_size / self.size * self.partition_num)
+        dist_index = math.floor(self.record_size * 1. / self.size * self.partition_num)
         # issue 1 by @camigord
-        partition_size = math.floor(self.size / self.partition_num)
+        partition_size = math.floor(self.size * 1. / self.partition_num)
         partition_max = dist_index * partition_size
         distribution = self.distributions[dist_index]
         rank_list = []
         # sample from k segments
         for n in range(1, self.batch_size + 1):
-            index = random.randint(distribution['strata_ends'][n] + 1,
-                                   distribution['strata_ends'][n + 1])
+            index = random.randint(distribution['strata_ends'][n],
+                                       distribution['strata_ends'][n + 1])
             rank_list.append(index)
 
         # beta, increase by global_step, max 1
diff --git a/tianshou/data/replay_buffer/replay_buffer_test.py b/tianshou/data/replay_buffer/replay_buffer_test.py
index 9be659b..46b25c8 100644
--- a/tianshou/data/replay_buffer/replay_buffer_test.py
+++ b/tianshou/data/replay_buffer/replay_buffer_test.py
@@ -1,13 +1,15 @@
-from utils import *
 from functions import *
 
+from tianshou.data.replay_buffer.utils import get_replay_buffer
+
+
 def test_rank_based():
     conf = {'size': 50,
             'learn_start': 10,
             'partition_num': 5,
             'total_step': 100,
             'batch_size': 4}
-    experience = getReplayBuffer('rank_based', conf)
+    experience = get_replay_buffer('rank_based', conf)
 
     # insert to experience
     print 'test insert experience'
@@ -52,7 +54,7 @@ def test_proportional():
     conf = {'size': 50,
             'alpha': 0.7,
             'batch_size': 4}
-    experience = getReplayBuffer('proportional', conf)
+    experience = get_replay_buffer('proportional', conf)
 
     # insert to experience
     print 'test insert experience'
@@ -90,7 +92,7 @@ def test_proportional():
 
 def test_naive():
     conf = {'size': 50}
-    experience = getReplayBuffer('naive', conf)
+    experience = get_replay_buffer('naive', conf)
 
     # insert to experience
     print 'test insert experience'
diff --git a/tianshou/data/replay_buffer/utils.py b/tianshou/data/replay_buffer/utils.py
index 3bb9bfe..4480375 100644
--- a/tianshou/data/replay_buffer/utils.py
+++ b/tianshou/data/replay_buffer/utils.py
@@ -1,17 +1,20 @@
-from rank_based import *
-from proportional import *
-from naive import *
 import sys
 
-def getReplayBuffer(name, conf):
-	'''
-	Get replay buffer according to the given name.
-	'''
-	if (name == 'rank_based'):
-		return RankBasedExperience(conf)
-	elif (name == 'proportional'):
-		return PropotionalExperience(conf)
-	elif (name == 'naive'):
-		return NaiveExperience(conf)
-	else:
-		sys.stderr.write('no such replay buffer')
+from tianshou.data.replay_buffer.naive import NaiveExperience
+from tianshou.data.replay_buffer.proportional import PropotionalExperience
+from tianshou.data.replay_buffer.rank_based import RankBasedExperience
+
+
+def get_replay_buffer(name, env, policy, qnet, target_qnet, conf):
+    """
+    Get replay buffer according to the given name.
+    """
+
+    if name == 'rank_based':
+        return RankBasedExperience(env, policy, qnet, target_qnet, conf)
+    elif name == 'proportional':
+        return PropotionalExperience(env, policy, qnet, target_qnet, conf)
+    elif name == 'naive':
+        return NaiveExperience(env, policy, qnet, target_qnet, conf)
+    else:
+        sys.stderr.write('no such replay buffer')