diff --git a/python/paddle/fluid/dygraph/dygraph_to_static/utils.py b/python/paddle/fluid/dygraph/dygraph_to_static/utils.py
index ed7faf83cefe5d21b03509f54132119577308d36..d3db7209c659d035bbabf67fd54c40a3db954746 100644
--- a/python/paddle/fluid/dygraph/dygraph_to_static/utils.py
+++ b/python/paddle/fluid/dygraph/dygraph_to_static/utils.py
@@ -156,7 +156,12 @@ def create_undefined_variable():
     from paddle.fluid.dygraph.dygraph_to_static.return_transformer import RETURN_NO_VALUE_MAGIC_NUM
     var = data_layer_not_check(unique_name.generate("undefined_var"), [1],
                                "float64")
+    # the variable is created in block(0), we append assign in block(0) either.
+    helper = LayerHelper('create_undefined_variable', **locals())
+    saved_block_ids = helper.main_program.current_block_idx
+    helper.main_program.current_block_idx = 0
     assign(RETURN_NO_VALUE_MAGIC_NUM, var)
+    helper.main_program.current_block_idx = saved_block_ids
     return var
 
 
diff --git a/python/paddle/fluid/layers/control_flow.py b/python/paddle/fluid/layers/control_flow.py
index d7b859612473f50a473f50b03af9a999f30dd065..4a2cab2e062d8c85ab7482cef7f6d42292f9e2a7 100755
--- a/python/paddle/fluid/layers/control_flow.py
+++ b/python/paddle/fluid/layers/control_flow.py
@@ -1161,6 +1161,8 @@ class While(object):
             if inner_var:
                 out_vars.append(inner_var)
 
+        x_name_list |= set(map(lambda x: x.name, out_vars))
+
         step_scope = parent_block.create_var(
             type=core.VarDesc.VarType.STEP_SCOPES)
 
diff --git a/python/paddle/fluid/tests/unittests/test_while_op.py b/python/paddle/fluid/tests/unittests/test_while_op.py
index 8e35a57f2426f543e862a757af98f2620c74039a..04093fdceb312f09f8bd3452fd094b36a212309f 100644
--- a/python/paddle/fluid/tests/unittests/test_while_op.py
+++ b/python/paddle/fluid/tests/unittests/test_while_op.py
@@ -190,5 +190,44 @@ class TestIgnoreVarNameInWhile(unittest.TestCase):
         self.assertListEqual(list(res.shape), [3, 1, 5])
 
 
+class TestOutputsMustExistsInputs(unittest.TestCase):
+
+    def test_outputs_exists_inputs(self):
+        """
+        We guarantee that the output tensor must be in the input tensor, so that the output and input can correspond to each other, but the input can be greater than the number of outputs. It's required in paddle2onnx.
+        """
+        main_program = fluid.Program()
+        startup_program = fluid.Program()
+        with fluid.program_guard(main_program, startup_program):
+
+            def func(x):
+                s = paddle.zeros([1])
+                i = paddle.ones([1])
+                max_len = paddle.shape(x)[0]
+
+                def cond(i, s, x):
+                    return i < max_len
+
+                def body(i, s, x):
+                    iter = x[i]
+                    s += iter
+                    i += 1
+                    return i, s, x
+
+                [i, s, x] = paddle.static.nn.while_loop(cond, body, [i, s, x])
+                return s
+
+            paddle.enable_static()
+            x = paddle.static.data(shape=[-1], name='x')
+            func(x)
+        for op in main_program.block(0).ops:
+            if op.type == "while":
+                for out_name in op.output("Out"):
+                    self.assertTrue(
+                        out_name in op.input("X"),
+                        "In while op, the variable in output(`Out`) must exists in inputs(`X`), but the variable with name `{}` not meet the precondition."
+                        .format(out_name))
+
+
 if __name__ == '__main__':
     unittest.main()