The force state of balance weight is directly changed when the water flow is unstable,which is affecting the stability of the ship’s operation.Therefore,it is an effective way to improve the quality of ship lift operation by choosing a reasonable balance weight’s body form at the bottom.In this paper,the 3D coupling fluid-structure-coupled mathematical model of the different balance weight’s body form at the bottom is designed and built,which can dynamically simulate the hydrodynamic response when balance weight is lifted up and down under the action of unsteady flow.The results show that the effect of the flow on the bottom of the balance weight is improved,the horizontal force is almost disappeared,the flow velocity between the gaps is evenly distributed ,and the balance weight wave problem is resolved.