The length-width ratio of the navigation lock of downstream water level regulation project for Shuikou hydro-junction reaches 16.7:1, and the filling time is required to be short, the hydraulic indexes are required to be quite high. According to the Design Code for Filling and Emptying System of Locks and the practical situation, the type of filling and emptying system of this lock is put forward, the main dimensions and detailed layout are designed, the hydraulic characteristics, valve’s working conditions, and vessel’s berthing conditions in lock chamber and upstream and downstream approach channels are all computed and analyzed. The results indicate that all the hydraulic characteristics satisfy the requirements of the code and design.