diff --git a/python/paddle/fluid/layers/utils.py b/python/paddle/fluid/layers/utils.py
index 702cb8464adb8547458905bd434c241822af7e8a..d5c0310d16579e27714eaf44242bf1a366295ae8 100644
--- a/python/paddle/fluid/layers/utils.py
+++ b/python/paddle/fluid/layers/utils.py
@@ -17,7 +17,7 @@ import collections
 import copy
 import six
 import numpy as np
-from ..framework import Variable, in_dygraph_mode
+from ..framework import Block, Variable, in_dygraph_mode
 from ..data_feeder import convert_dtype, check_variable_and_dtype, check_type, check_dtype
 from ..layer_helper import LayerHelper
 from sys import version_info
@@ -429,3 +429,31 @@ def try_get_constant_shape_from_tensor(shape_tensor):
             return None
 
         return None
+
+
+def get_inputs_outputs_in_block(block):
+    """
+    Returns the inputs and outputs variable used in this block but not
+    created in this block.
+    """
+    assert isinstance(
+        block,
+        Block), "input non-Block argument for get_inputs_outputs_in_block."
+    assert block.parent_idx != -1, "input block should be a sub-block, not main block."
+
+    # Find input/output var names of all ops in block
+    inner_inputs = set()
+    inner_outputs = set()
+    for op in block.ops:
+        for iname in op.input_names:
+            for in_var_name in op.input(iname):
+                if not block.has_var(in_var_name):
+                    # variable not created in this block
+                    inner_inputs.add(in_var_name)
+        for oname in op.output_names:
+            for out_var_name in op.output(oname):
+                if not block.has_var(out_var_name):
+                    # variable not created in this block
+                    inner_outputs.add(out_var_name)
+
+    return inner_inputs, inner_outputs
diff --git a/python/paddle/fluid/tests/unittests/test_get_inputs_outputs_in_block.py b/python/paddle/fluid/tests/unittests/test_get_inputs_outputs_in_block.py
new file mode 100644
index 0000000000000000000000000000000000000000..9e82057959408002fe7c26d8c10be37a27c56d6b
--- /dev/null
+++ b/python/paddle/fluid/tests/unittests/test_get_inputs_outputs_in_block.py
@@ -0,0 +1,78 @@
+#   Copyright (c) 2021 PaddlePaddle 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 __future__ import print_function
+
+import unittest
+import paddle
+import numpy as np
+from paddle.fluid.layers import utils
+
+paddle.enable_static()
+
+
+class TestGetInputsOutputsInBlock(unittest.TestCase):
+    def test_ordered(self):
+        # Program variable names may be different when test order is different
+        # This helper makes the test ordered.
+        self._test_while_loop()
+        self._test_cond()
+
+    def _test_while_loop(self):
+        main_program = paddle.static.Program()
+        startup_program = paddle.static.Program()
+        with paddle.static.program_guard(main_program, startup_program):
+            i = paddle.assign(np.array([1]))
+            ten = paddle.assign(np.array([10]))
+
+            def while_cond(i):
+                # use ten in parent block without passing it
+                return i < ten
+
+            def while_body(i):
+                # variable created in sub block
+                one = paddle.assign(np.array([1]))
+                i = i + one
+                return [i]
+
+            i = paddle.static.nn.while_loop(while_cond, while_body, [i])
+
+        sub_block = main_program.block(1)
+        inner_inputs, inner_outputs = utils.get_inputs_outputs_in_block(
+            sub_block)
+        # 'assign_0.tmp_0', 'assign_1.tmp_0' are name of i and ten in program
+        self.assertTrue(inner_inputs == {'assign_0.tmp_0', 'assign_1.tmp_0'})
+        # 'tmp_0', 'assign_0.tmp_0' are name of i < ten and i in program
+        self.assertTrue(inner_outputs == {'tmp_0', 'assign_0.tmp_0'})
+
+    def _test_cond(self):
+        main_program = paddle.static.Program()
+        startup_program = paddle.static.Program()
+        with paddle.static.program_guard(main_program, startup_program):
+            a = paddle.zeros((1, 1))
+            b = paddle.zeros((1, 1))
+            c = a * b
+            out = paddle.static.nn.cond(a < b, lambda: a + c, lambda: b * b)
+
+        sub_block = main_program.block(1)
+        inner_inputs, inner_outputs = utils.get_inputs_outputs_in_block(
+            sub_block)
+        #'fill_constant_1.tmp_0', 'tmp_3' are names of a, c 
+        self.assertTrue(inner_inputs == {'fill_constant_1.tmp_0', 'tmp_3'})
+        #'_generated_var_1', is name of a + c
+        self.assertTrue(inner_outputs == {'_generated_var_1'})
+
+
+if __name__ == "__main__":
+    unittest.main()