diff --git a/colossalai/autochunk/index_tracer.py b/colossalai/autochunk/index_tracer.py
index 0323e3a7e..221217e2d 100644
--- a/colossalai/autochunk/index_tracer.py
+++ b/colossalai/autochunk/index_tracer.py
@@ -812,19 +812,7 @@ class IndexTracer(object):
             cur_node_list = next_node_list
         return all_node_info
 
-    def flow_search(self, start_idx, start_dim, end_idx, end_dim):
-        inputs, outputs = find_chunk_compute_input_and_output_nodes(
-            self.node_list[start_idx : end_idx + 1]
-        )
-        # only single ouput
-        if len(outputs) > 1:
-            return None
-
-        # get every node's chunk dim and fix dim
-        all_node_info = self._get_all_node_info(end_dim, start_idx, end_idx)
-        if all_node_info is None:
-            return None
-
+    def _get_input_nodes_dim(self, inputs, start_idx, end_idx, all_node_info):
         inputs_dim = []
         remove_inputs = []
         for input_node in inputs:
@@ -841,7 +829,7 @@ class IndexTracer(object):
                         if input_node_idx in user_source:
                             input_dict[user_idx] = user_source[input_node_idx]
                         else:
-                            return None
+                            return None, None
             if len(input_dict) == 0:
                 remove_inputs.append(input_node)
             else:
@@ -849,6 +837,25 @@ class IndexTracer(object):
         for i in remove_inputs:
             if i in inputs:
                 inputs.remove(i)
+        return inputs, inputs_dim
+
+    def flow_search(self, start_idx, start_dim, end_idx, end_dim):
+        inputs, outputs = find_chunk_compute_input_and_output_nodes(
+            self.node_list[start_idx : end_idx + 1]
+        )
+        # only single ouput
+        if len(outputs) > 1:
+            return None
+
+        # get every node's chunk dim and fix dim
+        all_node_info = self._get_all_node_info(end_dim, start_idx, end_idx)
+        if all_node_info is None:
+            return None
+
+        # get input nodes' chunk dim
+        inputs, inputs_dim = self._get_input_nodes_dim(inputs, start_idx, end_idx, all_node_info)
+        if inputs is None:
+            return None
 
         chunk_info = {
             "region": (start_idx, end_idx),