The downstream approach channel of Three Gorges ship lift has the characteristics of large fluctuation of water level and fast change rate. To reduce the influence of water level change on downstream docking operation of the ship of Three Gorges ship lift,we establish a mathematical expression of fitting for the water depth of ship and the deviation between ship and the downstream when docking downstream of the ship by using the least squares fitting method.It is concluded that the water depth of ship and the deviation between ship and the downstream are linearly corresponding when docking downstream of the ship.According to the current operation status of Three Gorges ship lift,and the variation of the water depth of ship,the deviation between ship and the downstream,we propose the operational strategies for different periods of docking downstream of the ship to provide experience for the operation of the Three Gorges ship lift.