diff --git a/colossalai/autochunk/index_tracer.py b/colossalai/autochunk/index_tracer.py
index 221217e2d..206d2edbd 100644
--- a/colossalai/autochunk/index_tracer.py
+++ b/colossalai/autochunk/index_tracer.py
@@ -839,36 +839,7 @@ class IndexTracer(object):
                 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),
-            "inputs": inputs,
-            "inputs_non_chunk": [],
-            "inputs_dim": inputs_dim,
-            "outputs": outputs,
-            "outputs_dim": end_dim,
-            "node_chunk_dim": all_node_info,
-            "args": {},
-        }
-
-        # move useless nodes ahead of loop
+    def _set_prepose_nodes(self, all_node_info, start_idx, end_idx):
         # get all possible prepose nodes
         maybe_prepose_nodes = []
         for node, node_info in all_node_info.items():
@@ -929,12 +900,45 @@ class IndexTracer(object):
                         maybe_prepose_nodes.remove(n)
         # sort by index
         prepose_nodes.sort(key=lambda x: find_idx_by_name(x.name, self.node_list))
-        chunk_info["args"]["prepose_nodes"] = prepose_nodes
+
+        return prepose_nodes
+    
+    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),
+            "inputs": inputs,
+            "inputs_non_chunk": [],
+            "inputs_dim": inputs_dim,
+            "outputs": outputs,
+            "outputs_dim": end_dim,
+            "node_chunk_dim": all_node_info,
+            "args": {},
+        }
+
+        # move useless nodes ahead of loop
+        chunk_info["args"]["prepose_nodes"] = self._set_prepose_nodes(all_node_info, start_idx, end_idx)
 
         # we need to log input nodes to avoid deleteing them in the loop
         chunk_node_list = self.node_list[start_idx : end_idx + 1]
         # also need to get some prepose node's arg out of non_chunk_inputs
-        for n in prepose_nodes:
+        for n in chunk_info["args"]["prepose_nodes"]:
             chunk_node_list.remove(n)
         non_chunk_inputs = find_chunk_all_input_nodes(chunk_node_list)
         for i in non_chunk_inputs: