Aiming at the problem of navigation-obstructing flow in Xiongcheng reach of the middle Yangtze River，we use a mathematical model to study the flow characteristics of the reach.The results show that the riverway is narrow and curved，the beach is not high，and affected by the outflow of Dongting Lake，the three-dimensional characteristics of flow in Xiongcheng reach are obvious，and there are many flow structures such as crossflow，circulation and backflow，which have great influence on ship navigation.When the flow of the trunk line is 25,000 m3s to 30,000 m3s，and the water level of Dongting Lake is high，ship accidents are likely to occur，so it is necessary to remind ships to navigate with caution.