diff --git a/demo/agent/mock_sync.py b/demo/agent/mock_sync.py
index 74d871a..d95880c 100644
--- a/demo/agent/mock_sync.py
+++ b/demo/agent/mock_sync.py
@@ -815,8 +815,12 @@ def sync_to_central(pg, sp_id: int, contacts_data, run_counter: int = 1):
 
             for j, (sender_role, msg_type, content) in enumerate(messages):
                 local_id_counter += 1
-                # 时间递增：每条消息间隔 2～30 分钟
-                msg_time = base_time + time_offset + dt.timedelta(minutes=j * random.randint(2, 30))
+                # 时间递增：每条消息在前一条基础上累加 2～30 分钟，确保单调递增
+                if j == 0:
+                    cumulative_minutes = 0
+                else:
+                    cumulative_minutes += random.randint(2, 30)
+                msg_time = base_time + time_offset + dt.timedelta(minutes=cumulative_minutes)
 
                 if sender_role == "customer":
                     sender_wx = wx_username if not is_group else f"wxid_customer_{j}"