Based on the requirement of operation characteristics，the control valves of hydro-driven ship lift are designed as“one main and two auxiliary”combined valves，so multiple valves discharge water into the same finite cavity at the same time. In order to minimize the impact of multiple turbulent jets on the valve segment，how to distribute the flow of three valves is an urgent problem to solve. Based on the Jinghong hydro-driven ship lift and the valve section of the water filling system，a 3D numerical model is established to study the flow field characteristics of valve section under different operating modes of combined valves and discuss the relationship between combined valve operation mode and the flow field uniformity. The research results show that ：1）When the main valve and the auxiliary valve run alone or the main valve runs in combination with one auxiliary valve，there are obvious drift and vortex low pressure area in the valve section. 2）Under the rectifying and stabilizing pressure of sudden expansion，these adverse hydraulic phenomena will not endanger the operation safety of ship lift，but considering the rationality and efficiency of operation，these extreme working conditions should be avoided as far as possible. 3）Based on the analysis of flow field uniformity，it can be seen that three-valve joint operation is the best combined valves operation mode.