diff --git a/paddle/fluid/operators/controlflow/while_op.cc b/paddle/fluid/operators/controlflow/while_op.cc
index 6ccacddf070ed07bb6f1f1b96388f63c5cef718e..4e0344b3b939165baee3aef1ab2c36f37b356bf8 100644
--- a/paddle/fluid/operators/controlflow/while_op.cc
+++ b/paddle/fluid/operators/controlflow/while_op.cc
@@ -86,6 +86,19 @@ class WhileOp : public framework::OperatorBase {
 
     std::set<std::string> no_copy_var_names;
     if (!is_test) {
+      // set all persistable parameters into no_copy_var_names.
+      auto *global_block = block;
+
+      while (global_block->ID() != 0)
+        global_block = global_block->ParentBlock();
+      auto all_vars = global_block->AllVars();
+      std::for_each(all_vars.begin(),
+                    all_vars.end(),
+                    [&no_copy_var_names](framework::VarDesc *var) {
+                      if (var->IsParameter())
+                        no_copy_var_names.insert(var->Name());
+                    });
+
       const std::vector<framework::OpDesc *> &all_ops = block->AllOps();
       for (const framework::OpDesc *op : all_ops) {
         const framework::VariableNameMap &input_var_names = op->Inputs();
diff --git a/python/paddle/fluid/dygraph/dygraph_to_static/utils.py b/python/paddle/fluid/dygraph/dygraph_to_static/utils.py
index d3db7209c659d035bbabf67fd54c40a3db954746..09a249ed6b10fff009d5eb91017012be7fda09fb 100644
--- a/python/paddle/fluid/dygraph/dygraph_to_static/utils.py
+++ b/python/paddle/fluid/dygraph/dygraph_to_static/utils.py
@@ -148,7 +148,12 @@ def create_undefined_var_like(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"),
                                variable.shape, variable.dtype)
+    var.stop_gradient = False
+    helper = LayerHelper('create_undefined_var_like', **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
 
 
@@ -156,6 +161,7 @@ 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")
+    var.stop_gradient = False
     # 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
diff --git a/python/paddle/fluid/layers/control_flow.py b/python/paddle/fluid/layers/control_flow.py
index 43781665dc3ca924710b8cbc4ef3cfa418931743..258038fea6a453f1ef4b507f83455a63779722c0 100755
--- a/python/paddle/fluid/layers/control_flow.py
+++ b/python/paddle/fluid/layers/control_flow.py
@@ -89,9 +89,9 @@ def select_input(inputs, mask):
     check_type(inputs, 'inputs', (list, tuple), 'select_input')
     check_variable_and_dtype(mask, 'mask', ['int32'], 'select_input')
 
-    input_dtype = inputs[0].dtype
-    input_shape = inputs[0].shape
-    input_type = inputs[0].type
+    input_dtype = inputs[1].dtype
+    input_shape = inputs[1].shape
+    input_type = inputs[1].type
 
     out = helper.create_variable(dtype=input_dtype,
                                  shape=input_shape,
@@ -1190,6 +1190,13 @@ def assign_skip_lod_tensor_array(input, output):
     """
     Assign input to output, but skip the process of copying LoDTensorArray unless it's created in while_block.
     """
+
+    def has_shape_diff(x_var, y_var):
+        if len(x_var.shape) != len(y_var.shape): return True
+        for x_dim, y_dim in zip(x_var.shape, y_var.shape):
+            if x_dim != y_dim and -1 not in [x_dim, y_dim]: return True
+        return False
+
     if not isinstance(input, (Variable, core.VarBase)):
         if isinstance(output, Variable) and isinstance(
                 input, support_ret_buildin_type):
@@ -1205,6 +1212,11 @@ def assign_skip_lod_tensor_array(input, output):
         if parent_block and not parent_block._find_var_recursive(input.name):
             assign(input, output)
     else:
+        if isinstance(output, Variable) and isinstance(
+                input, Variable) and has_shape_diff(input, output):
+            warnings.warn(
+                "In dy2static mode, we attemp to assign a variable with shape {} into a variable with shape{}, which is not always right."
+                .format(input.shape, output.shape))
         assign(input, output)