In recent years, the downstream of Ganjiang river is infected by the sand-excavation on the river channel. The river bed and water level decline obviously. The shape of river channel has changed. The waterway regulation parameters have been infected. Based on the analysis of hydraulic characteristics and waterway regulation parameters, this paper calculates the lowest navigable water level for the hydrology station of Zhangshu, Fengcheng, Shicha and Waizhou. The variation of regulation width is calculated and compared with designed results.