diff --git a/README.md b/README.md
index 28ff004b39..3e2faa94da 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,8 @@
 Recent released features
 | Feature | Status |
 | --                      | ------    |
+| Point-in-Time database | :hammer: [Rleased](https://github.com/microsoft/qlib/pull/343) on Mar 10, 2022 |
+| Arctic Provider Backend & Orderbook data example | :hammer: [Rleased](https://github.com/microsoft/qlib/pull/744) on Jan 17, 2022 |
 | Arctic Provider Backend & Orderbook data example | :hammer: [Rleased](https://github.com/microsoft/qlib/pull/744) on Jan 17, 2022 |
 | Meta-Learning-based framework & DDG-DA  | :chart_with_upwards_trend:  :hammer: [Released](https://github.com/microsoft/qlib/pull/743) on Jan 10, 2022 | 
 | Planning-based portfolio optimization | :hammer: [Released](https://github.com/microsoft/qlib/pull/754) on Dec 28, 2021 | 
@@ -95,9 +97,8 @@ For more details, please refer to our paper ["Qlib: An AI-oriented Quantitative
 # Plans
 New features under development(order by estimated release time).
 Your feedbacks about the features are very important.
-| Feature                        | Status      |
-| --                      | ------    |
-| Point-in-Time database | Under review: https://github.com/microsoft/qlib/pull/343 |
+<!-- | Feature                        | Status      | -->
+<!-- | --                      | ------    | -->
 
 # Framework of Qlib
 
diff --git a/docs/index.rst b/docs/index.rst
index 9409d2ac19..f55262c027 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -53,6 +53,7 @@ Document Structure
    Online & Offline mode <advanced/server.rst>
    Serialization <advanced/serial.rst>
    Task Management <advanced/task_management.rst>
+   Point-In-Time database <advanced/PIT.rst>
 
 .. toctree::
    :maxdepth: 3
diff --git a/qlib/data/base.py b/qlib/data/base.py
index e93938f610..427c15e3ca 100644
--- a/qlib/data/base.py
+++ b/qlib/data/base.py
@@ -5,12 +5,8 @@
 from __future__ import division
 from __future__ import print_function
 
-import os
 import abc
 import pandas as pd
-import numpy as np
-
-from ..utils import code_to_fname
 from ..log import get_module_logger
 
 
@@ -270,5 +266,3 @@ class ExpressionOps(Expression):
     This kind of feature will use operator for feature
     construction on the fly.
     """
-
-    pass
diff --git a/qlib/data/cache.py b/qlib/data/cache.py
index 7d08e728df..fc6518de51 100644
--- a/qlib/data/cache.py
+++ b/qlib/data/cache.py
@@ -32,7 +32,7 @@
 )
 
 from ..log import get_module_logger
-from .base import Feature, PFeature
+from .base import Feature
 from .ops import Operators  # pylint: disable=W0611
 
 
diff --git a/qlib/data/data.py b/qlib/data/data.py
index aef27dbb25..cd8f7f77f6 100644
--- a/qlib/data/data.py
+++ b/qlib/data/data.py
@@ -6,7 +6,6 @@
 from __future__ import print_function
 
 import re
-import os
 import abc
 import copy
 import queue
@@ -24,7 +23,6 @@
 
 from ..log import get_module_logger
 from .cache import DiskDatasetCache
-from .base import Feature, PFeature
 from ..utils import (
     Wrapper,
     init_instance_by_config,
diff --git a/qlib/data/ops.py b/qlib/data/ops.py
index fd7eb94bb6..bdc032c037 100644
--- a/qlib/data/ops.py
+++ b/qlib/data/ops.py
@@ -1643,7 +1643,7 @@ def register_all_ops(C):
     """register all operator"""
     logger = get_module_logger("ops")
 
-    from qlib.data.pit import P
+    from qlib.data.pit import P  # pylint: disable=C0415
 
     Operators.reset()
     Operators.register(OpsList + [P])
diff --git a/qlib/data/pit.py b/qlib/data/pit.py
index 2cf144c6ef..4c38646b0c 100644
--- a/qlib/data/pit.py
+++ b/qlib/data/pit.py
@@ -17,11 +17,10 @@
 import pandas as pd
 from qlib.data.ops import ElemOperator
 from qlib.log import get_module_logger
-
+from .data import Cal
 
 class P(ElemOperator):
     def _load_internal(self, instrument, start_index, end_index, freq):
-        from .data import Cal
 
         _calendar = Cal.calendar(freq=freq)
         resample_data = np.empty(end_index - start_index + 1, dtype="float32")