diff --git a/tianshou/policy/modelfree/a2c.py b/tianshou/policy/modelfree/a2c.py
index e69cd15ba..9396971df 100644
--- a/tianshou/policy/modelfree/a2c.py
+++ b/tianshou/policy/modelfree/a2c.py
@@ -14,8 +14,7 @@ class A2CPolicy(PGPolicy):
     :param torch.nn.Module actor: the actor network following the rules in
         :class:`~tianshou.policy.BasePolicy`. (s -> logits)
     :param torch.nn.Module critic: the critic network. (s -> V(s))
-    :param torch.optim.Optimizer optim: the optimizer for actor and critic
-        network.
+    :param torch.optim.Optimizer optim: the optimizer for actor and critic network.
     :param dist_fn: distribution class for computing the action.
     :type dist_fn: Type[torch.distributions.Distribution]
     :param float discount_factor: in [0, 1]. Default to 0.99.
@@ -71,6 +70,13 @@ def __init__(
 
     def process_fn(
         self, batch: Batch, buffer: ReplayBuffer, indice: np.ndarray
+    ) -> Batch:
+        batch = self._compute_returns(batch, buffer, indice)
+        batch.act = to_torch_as(batch.act, batch.v_s)
+        return batch
+
+    def _compute_returns(
+        self, batch: Batch, buffer: ReplayBuffer, indice: np.ndarray
     ) -> Batch:
         v_s, v_s_ = [], []
         with torch.no_grad():
@@ -96,7 +102,6 @@ def process_fn(
             self.ret_rms.update(unnormalized_returns)
         else:
             batch.returns = unnormalized_returns
-        batch.act = to_torch_as(batch.act, batch.v_s)
         batch.returns = to_torch_as(batch.returns, batch.v_s)
         batch.adv = to_torch_as(advantages, batch.v_s)
         return batch
diff --git a/tianshou/policy/modelfree/ppo.py b/tianshou/policy/modelfree/ppo.py
index 0b2c76e2e..9b9c61272 100644
--- a/tianshou/policy/modelfree/ppo.py
+++ b/tianshou/policy/modelfree/ppo.py
@@ -4,7 +4,7 @@
 from typing import Any, Dict, List, Type, Optional
 
 from tianshou.policy import A2CPolicy
-from tianshou.data import Batch, ReplayBuffer, to_numpy, to_torch_as
+from tianshou.data import Batch, ReplayBuffer, to_torch_as
 
 
 class PPOPolicy(A2CPolicy):
@@ -24,6 +24,11 @@ class PPOPolicy(A2CPolicy):
         Default to 5.0 (set None if you do not want to use it).
     :param bool value_clip: a parameter mentioned in arXiv:1811.02553 Sec. 4.1.
         Default to True.
+    :param bool advantage_normalization: whether to do per mini-batch advantage
+        normalization. Default to True.
+    :param bool recompute_advantage: whether to recompute advantage every update
+        repeat according to https://arxiv.org/pdf/2006.05990.pdf Sec. 3.5.
+        Default to False.
     :param float vf_coef: weight for value loss. Default to 0.5.
     :param float ent_coef: weight for entropy loss. Default to 0.01.
     :param float max_grad_norm: clipping gradients in back propagation. Default to
@@ -59,7 +64,9 @@ def __init__(
         dist_fn: Type[torch.distributions.Distribution],
         eps_clip: float = 0.2,
         dual_clip: Optional[float] = None,
-        value_clip: bool = True,
+        value_clip: bool = False,
+        advantage_normalization: bool = True,
+        recompute_advantage: bool = False,
         **kwargs: Any,
     ) -> None:
         super().__init__(actor, critic, optim, dist_fn, **kwargs)
@@ -68,51 +75,41 @@ def __init__(
             "Dual-clip PPO parameter should greater than 1.0."
         self._dual_clip = dual_clip
         self._value_clip = value_clip
+        if not self._rew_norm:
+            assert not self._value_clip, \
+                "value clip is available only when `reward_normalization` is True"
+        self._norm_adv = advantage_normalization
+        self._recompute_adv = recompute_advantage
 
     def process_fn(
         self, batch: Batch, buffer: ReplayBuffer, indice: np.ndarray
     ) -> Batch:
-        v_s, v_s_, old_log_prob = [], [], []
+        if self._recompute_adv:
+            # buffer input `buffer` and `indice` to be used in `learn()`.
+            self._buffer = buffer
+            self._indice = indice
+        batch = self._compute_returns(batch, buffer, indice)
+        batch.act = to_torch_as(batch.act, batch.v_s)
+        old_log_prob = []
         with torch.no_grad():
             for b in batch.split(self._batch, shuffle=False, merge_last=True):
-                v_s.append(self.critic(b.obs))
-                v_s_.append(self.critic(b.obs_next))
-                old_log_prob.append(self(b).dist.log_prob(to_torch_as(b.act, v_s[0])))
-        batch.v_s = torch.cat(v_s, dim=0).flatten()  # old value
-        v_s = to_numpy(batch.v_s)
-        v_s_ = to_numpy(torch.cat(v_s_, dim=0).flatten())
-        # when normalizing values, we do not minus self.ret_rms.mean to be numerically
-        # consistent with OPENAI baselines' value normalization pipeline. Emperical
-        # study also shows that "minus mean" will harm performances a tiny little bit
-        # due to unknown reasons (on Mujoco envs, not confident, though).
-        if self._rew_norm:  # unnormalize v_s & v_s_
-            v_s = v_s * np.sqrt(self.ret_rms.var + self._eps)
-            v_s_ = v_s_ * np.sqrt(self.ret_rms.var + self._eps)
-        unnormalized_returns, advantages = self.compute_episodic_return(
-            batch, buffer, indice, v_s_, v_s,
-            gamma=self._gamma, gae_lambda=self._lambda)
-        if self._rew_norm:
-            batch.returns = unnormalized_returns / \
-                np.sqrt(self.ret_rms.var + self._eps)
-            self.ret_rms.update(unnormalized_returns)
-            mean, std = np.mean(advantages), np.std(advantages)
-            advantages = (advantages - mean) / std
-        else:
-            batch.returns = unnormalized_returns
-        batch.act = to_torch_as(batch.act, batch.v_s)
+                old_log_prob.append(self(b).dist.log_prob(b.act))
         batch.logp_old = torch.cat(old_log_prob, dim=0)
-        batch.returns = to_torch_as(batch.returns, batch.v_s)
-        batch.adv = to_torch_as(advantages, batch.v_s)
         return batch
 
     def learn(  # type: ignore
         self, batch: Batch, batch_size: int, repeat: int, **kwargs: Any
     ) -> Dict[str, List[float]]:
         losses, clip_losses, vf_losses, ent_losses = [], [], [], []
-        for _ in range(repeat):
+        for step in range(repeat):
+            if self._recompute_adv and step > 0:
+                batch = self._compute_returns(batch, self._buffer, self._indice)
             for b in batch.split(batch_size, merge_last=True):
                 # calculate loss for actor
                 dist = self(b).dist
+                if self._norm_adv:
+                    mean, std = b.adv.mean(), b.adv.std()
+                    b.adv = (b.adv - mean) / std  # per-batch norm
                 ratio = (dist.log_prob(b.act) - b.logp_old).exp().float()
                 ratio = ratio.reshape(ratio.size(0), -1).transpose(0, 1)
                 surr1 = ratio * b.adv
@@ -130,9 +127,9 @@ def learn(  # type: ignore
                         -self._eps_clip, self._eps_clip)
                     vf1 = (b.returns - value).pow(2)
                     vf2 = (b.returns - v_clip).pow(2)
-                    vf_loss = 0.5 * torch.max(vf1, vf2).mean()
+                    vf_loss = torch.max(vf1, vf2).mean()
                 else:
-                    vf_loss = 0.5 * (b.returns - value).pow(2).mean()
+                    vf_loss = (b.returns - value).pow(2).mean()
                 # calculate regularization and overall loss
                 ent_loss = dist.entropy().mean()
                 loss = clip_loss + self._weight_vf * vf_loss \