diff --git a/README.md b/README.md
index 4771378..ad7b5e0 100644
--- a/README.md
+++ b/README.md
@@ -115,7 +115,7 @@ You can check out the [documentation](https://tianshou.readthedocs.io) for furth
 
 ## Quick Start
 
-This is an example of Policy Gradient. You can also run the full script under [test/discrete/test_pg.py](/test/discrete/test_pg.py).
+This is an example of Deep Q Network. You can also run the full script under [test/discrete/test_dqn.py](/test/discrete/test_dqn.py).
 
 First, import the relevant packages:
 
@@ -123,56 +123,31 @@ First, import the relevant packages:
 import gym, torch, numpy as np, torch.nn as nn
 from torch.utils.tensorboard import SummaryWriter
 
-from tianshou.policy import PGPolicy
+from tianshou.policy import DQNPolicy
 from tianshou.env import SubprocVectorEnv
-from tianshou.trainer import onpolicy_trainer
+from tianshou.trainer import offpolicy_trainer
 from tianshou.data import Collector, ReplayBuffer
 ```
 
 Define some hyper-parameters:
 
 ```python
-task = 'CartPole-v0' 
-seed = 1626 
-lr = 3e-4 
-gamma = 0.9 
-epoch = 10 
-step_per_epoch = 1000 
-collect_per_step = 10 
-repeat_per_collect = 2 
-batch_size = 64 
-train_num = 8 
-test_num = 100 
-device = 'cuda' if torch.cuda.is_available() else 'cpu'
-writer = SummaryWriter('log/pg')  # tensorboard is also supported!
+task = 'CartPole-v0'
+lr = 1e-3
+gamma = 0.9
+n_step = 3
+eps_train, eps_test = 0.1, 0.05
+epoch = 10
+step_per_epoch = 1000
+collect_per_step = 10
+target_freq = 320
+batch_size = 64
+train_num, test_num = 8, 100
+buffer_size = 20000
+writer = SummaryWriter('log/dqn')  # tensorboard is also supported!
 ```
 
-Define the network:
-
-```python
-class Net(nn.Module):
-    def __init__(self, layer_num, state_shape, action_shape=0, device='cpu'):
-        super().__init__()
-        self.device = device
-        self.model = [
-            nn.Linear(np.prod(state_shape), 128),
-            nn.ReLU(inplace=True)]
-        for i in range(layer_num):
-            self.model += [nn.Linear(128, 128), nn.ReLU(inplace=True)]
-        if action_shape:
-            self.model += [nn.Linear(128, np.prod(action_shape))]
-        self.model = nn.Sequential(*self.model)
-
-    def forward(self, s, state=None, info={}):
-        if not isinstance(s, torch.Tensor):
-            s = torch.tensor(s, device=self.device, dtype=torch.float)
-        batch = s.shape[0]
-        s = s.view(batch, -1)
-        logits = self.model(s)
-        return logits, state
-```
-
-Make envs and fix seed:
+Make envs:
 
 ```python
 env = gym.make(task)
@@ -180,46 +155,68 @@ state_shape = env.observation_space.shape or env.observation_space.n
 action_shape = env.action_space.shape or env.action_space.n
 train_envs = SubprocVectorEnv([lambda: gym.make(task) for _ in range(train_num)])
 test_envs = SubprocVectorEnv([lambda: gym.make(task) for _ in range(test_num)])
-np.random.seed(seed)
-torch.manual_seed(seed)
-train_envs.seed(seed)
-test_envs.seed(seed)
 ```
 
-Setup policy and collector:
+Define the network:
 
 ```python
-net = Net(3, state_shape, action_shape, device).to(device)
+class Net(nn.Module):
+    def __init__(self, state_shape, action_shape):
+        super().__init__()
+        self.model = nn.Sequential(*[
+            nn.Linear(np.prod(state_shape), 128), nn.ReLU(inplace=True),
+            nn.Linear(128, 128), nn.ReLU(inplace=True),
+            nn.Linear(128, 128), nn.ReLU(inplace=True),
+            nn.Linear(128, np.prod(action_shape))
+        ])
+    def forward(self, s, state=None, info={}):
+        if not isinstance(s, torch.Tensor):
+            s = torch.tensor(s, dtype=torch.float)
+        batch = s.shape[0]
+        logits = self.model(s.view(batch, -1))
+        return logits, state
+
+net = Net(state_shape, action_shape)
 optim = torch.optim.Adam(net.parameters(), lr=lr)
-policy = PGPolicy(net, optim, torch.distributions.Categorical, gamma)
-train_collector = Collector(policy, train_envs, ReplayBuffer(20000))
+```
+
+Setup policy and collectors:
+
+```python
+policy = DQNPolicy(net, optim, gamma, n_step,
+                   use_target_network=True, target_update_freq=target_freq)
+train_collector = Collector(policy, train_envs, ReplayBuffer(buffer_size))
 test_collector = Collector(policy, test_envs)
 ```
 
 Let's train it:
 
 ```python
-result = onpolicy_trainer(policy, train_collector, test_collector, epoch, step_per_epoch, collect_per_step, repeat_per_collect, test_num, batch_size, stop_fn=lambda x: x >= env.spec.reward_threshold, writer=writer)
+result = offpolicy_trainer(
+    policy, train_collector, test_collector, epoch, step_per_epoch, collect_per_step,
+    test_num, batch_size, train_fn=lambda e: policy.set_eps(eps_train),
+    test_fn=lambda e: policy.set_eps(eps_test),
+    stop_fn=lambda x: x >= env.spec.reward_threshold, writer=writer, task=task)
 ```
 
 Saving / loading trained policy (it's exactly the same as PyTorch nn.module):
 
 ```python
-torch.save(policy.state_dict(), 'pg.pth')
-policy.load_state_dict(torch.load('pg.pth', map_location=device))
+torch.save(policy.state_dict(), 'dqn.pth')
+policy.load_state_dict(torch.load('dqn.pth'))
 ```
 
 Watch the performance with 35 FPS:
 
 ```python3
-collecter = Collector(policy, env)
-collecter.collect(n_episode=1, render=1/35)
+collector = Collector(policy, env)
+collector.collect(n_episode=1, render=1/35)
 ```
 
 Looking at the result saved in tensorboard: (on bash script)
 
 ```bash
-tensorboard --logdir log/pg
+tensorboard --logdir log/dqn
 ```
 
 ## Citing Tianshou