The dynamic water load in the discharge valve section of a ship lock is a key technical problem in the design of a high head ship lock. Based on the unsteady flow atmospheric pressure model test of the“flat bottom & expanding top”corridor of the back arc-gate of Qianwei ship lock，we emphatically study the characteristics of hydrodynamic pressure and hoisting force in valve section，hydro-dynamic load in the corridor of valve section under the condition of hydro-dynamic closing，the influence of opening rate and acting head on hydro-dynamic load and hoisting force. The results show that considering the structural system of valve，dynamic water load behind the door，characteristics of opening and closing force，air defense effect，the valve of Qianwei ship lock will not cause harmful flow-induced vibration.