The water-stop board of lying down small gate plays the role of separating the head of lock and the water body of hull,and its sealing tightness affects the safe operation of the Three Gorges ship lift.We apply the formula of collision force of ship against pier and abutment in Fundamental Code for Design on Railway Bridge and Culvert to calculate the equivalent impact force of the ship’s frontal impact on the water-stop board of lying down small gate under normal operating condition,use the software of Solidworks and ANSYS Workbench respectively to model and strain analysis of the water-stop board of lying down small gate,propose two optimal transformation schemes of small plate closure and whole plate closure,and compare with the difficulty of construction process and structural strength respectively.The results show that the whole plate closure is optimal scheme,which is suitable for the general working condition of the site.