The design of approach channel has great influence on general layout of locks.When a lock is constructed in rivers,the guard wall is arranged normally between the lock and weir or power house to guard the approach channel from the river flow,thus the favorable condition of water flow is formed.From the angle of guard wall layout,it is emphasized that the different criterions of the navigation flow conditions should be used for different locations of the entrance.The effects of covering the approach channel and reducing the crosscurrent are showed through analyzing the length and location of the guard wall.Then the different alternatives of layout of Shihutang lock are introduced.