Now,hydro-floating ship Lift has not run at practice in China and abroad,even we have no experiences to design,install and operate.In this paper,the fluid-structure-coupled mathematical model of different clearance ratio between the silo current and the balance weight is designed and built,which can dynamically simulates the hydrodynamic response when balance weight is lifted up and down under the action of unsteady flow.And then,the optimal clearance ratio is obtained for the stable operation of the ship lift