diff --git a/oneflow/api/python/framework/doc.cpp b/oneflow/api/python/framework/doc.cpp
new file mode 100644
index 00000000000..9ee66b4f3de
--- /dev/null
+++ b/oneflow/api/python/framework/doc.cpp
@@ -0,0 +1,45 @@
+/*
+Copyright 2020 The OneFlow Authors. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+#include <pybind11/pybind11.h>
+
+#include "oneflow/api/python/of_api_registry.h"
+#include "oneflow/api/python/framework/throw.h"
+
+namespace py = pybind11;
+
+namespace oneflow {
+
+py::object AddFunctionDoc(py::object f, const std::string& doc_string) {
+  static std::vector<std::string> all_doc_strings;
+  all_doc_strings.emplace_back(doc_string);
+  const char* doc_str = all_doc_strings.back().c_str();
+  PyObject* obj = f.ptr();
+  if (PyCFunction_Check(obj)) {
+    auto* f = (PyCFunctionObject*)obj;
+    if (f->m_ml->ml_doc) {
+      THROW(RuntimeError) << "function " << f->m_ml->ml_name << " already has a docstring.";
+    }
+    f->m_ml->ml_doc = doc_str;
+  } else {
+    THROW(RuntimeError) << "function is " << Py_TYPE(obj)->tp_name << ", not a valid PyCFunction.";
+  }
+  f.inc_ref();
+  return f;
+}
+
+}  // namespace oneflow
+
+ONEFLOW_API_PYBIND11_MODULE("", m) { m.def("add_doc", &oneflow::AddFunctionDoc); }
diff --git a/python/oneflow/F/__init__.py b/python/oneflow/F/__init__.py
index e69de29bb2d..419121d74e9 100644
--- a/python/oneflow/F/__init__.py
+++ b/python/oneflow/F/__init__.py
@@ -0,0 +1,16 @@
+"""
+Copyright 2020 The OneFlow Authors. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+from oneflow._oneflow_internal.F import *
diff --git a/python/oneflow/__init__.py b/python/oneflow/__init__.py
index ae96ea9d3f6..8b70197fa84 100644
--- a/python/oneflow/__init__.py
+++ b/python/oneflow/__init__.py
@@ -141,12 +141,10 @@ def atexit_hook(hook):
 del ExitHook
 del atexit
 del oneflow
+
+import oneflow.F
 import oneflow.framework.docstr as docstr
-from oneflow.framework.docstr.utils import register_docstr
 
-register_docstr()
-del register_docstr
-del docstr
 from oneflow.autograd import grad_enable, no_grad, inference_mode, is_grad_enabled
 import oneflow.nn.image
 import oneflow.nn.modules.acosh
diff --git a/python/oneflow/framework/docstr/utils.py b/python/oneflow/framework/docstr/utils.py
index 8cfc557af15..301610c8d1e 100644
--- a/python/oneflow/framework/docstr/utils.py
+++ b/python/oneflow/framework/docstr/utils.py
@@ -13,13 +13,9 @@
 See the License for the specific language governing permissions and
 limitations under the License.
 """
-_function_docstr = {}
 
-
-def add_docstr(fun, docstr: str):
-    _function_docstr[fun] = docstr
+import oneflow._oneflow_internal
 
 
-def register_docstr():
-    for (fun, docstr) in _function_docstr.items():
-        setattr(fun, "__doc__", docstr)
+def add_docstr(fun, docstr: str):
+    return oneflow._oneflow_internal.add_doc(fun, docstr)
diff --git a/python/oneflow/framework/functional.py b/python/oneflow/framework/functional.py
deleted file mode 100644
index 95e7cdc1e26..00000000000
--- a/python/oneflow/framework/functional.py
+++ /dev/null
@@ -1,45 +0,0 @@
-"""
-Copyright 2020 The OneFlow Authors. All rights reserved.
-
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
-"""
-import oneflow as flow
-import oneflow._oneflow_internal
-
-
-class Function:
-    def __init__(self, func_name, handle):
-        self.func_name = func_name
-        self.handle = handle
-
-    def __call__(self, *args, **kwargs):
-        return self.handle(*args, **kwargs)
-
-
-def RegisterFunctionalApis():
-    import inspect
-
-    import oneflow.F
-
-    for s in dir(oneflow._oneflow_internal.F):
-        f = getattr(oneflow._oneflow_internal.F, s)
-        if inspect.isbuiltin(f):
-            func_name = s
-            if s in _function_name_aliases:
-                func_name = _function_name_aliases[s]
-                setattr(oneflow.F, func_name, Function(func_name, f))
-            setattr(oneflow.F, s, Function(func_name, f))
-    del inspect
-
-
-_function_name_aliases = {"add_scalar": "scalar_add"}
diff --git a/python/oneflow/framework/register_class_method_util.py b/python/oneflow/framework/register_class_method_util.py
index dd53ba0f87e..fce74ed0ca5 100644
--- a/python/oneflow/framework/register_class_method_util.py
+++ b/python/oneflow/framework/register_class_method_util.py
@@ -14,7 +14,6 @@
 limitations under the License.
 """
 import oneflow._oneflow_internal
-import oneflow.framework.functional as functional
 import oneflow.framework.generator as generator
 import oneflow.framework.op_expr_util as op_expr_util
 import oneflow.framework.tensor as tensor_util
@@ -23,4 +22,3 @@
 def RegisterMethod4Class():
     tensor_util.RegisterMethods()
     op_expr_util.RegisterMethod4UserOpExpr()
-    functional.RegisterFunctionalApis()
diff --git a/python/oneflow/test/modules/test_functional_docstr.py b/python/oneflow/test/modules/test_functional_docstr.py
index 0634db793ca..fdb4a4961ca 100644
--- a/python/oneflow/test/modules/test_functional_docstr.py
+++ b/python/oneflow/test/modules/test_functional_docstr.py
@@ -22,11 +22,6 @@
 
 import oneflow as flow
 import oneflow.unittest
-from oneflow.framework.functional import Function
-
-
-def _is_oneflow_functional(object):
-    return isinstance(object, Function)
 
 
 def _run_functional_doctest(
@@ -44,7 +39,7 @@ def _run_functional_doctest(
         runner = doctest.DebugRunner(verbose=verbose, optionflags=optionflags)
     else:
         runner = doctest.DocTestRunner(verbose=verbose, optionflags=optionflags)
-    r = inspect.getmembers(flow.F, _is_oneflow_functional)
+    r = inspect.getmembers(flow.F)
     for (name, fun) in r:
         if fun.__doc__ is not None:
             print("test on docstr of: ", ".".join([module.__name__, name]))
diff --git a/tools/generate_functional_api.py b/tools/generate_functional_api.py
index a9195c0ba0b..0796473404d 100644
--- a/tools/generate_functional_api.py
+++ b/tools/generate_functional_api.py
@@ -121,7 +121,11 @@
 namespace functional = one::functional;
 
 ONEFLOW_API_PYBIND11_MODULE("F", m) {{
+  py::options options;
+  options.disable_function_signatures();
+
 {1}
+  options.enable_function_signatures();
 }}
 
 }}  // namespace oneflow