The continuous low water level of Poyang Lake has had a significant impact on people’s life, water ecology and water environment in the lake area since 2003. Based on a series of measured hydrological data, the causes and trends of the variation of water level in low-water season are analyzed in terms of rainfall in the basin, reservoir storage in the main and tributary reservoirs in the upper reaches of the Yangtze River, scouring in waterway of Poyang Lake to Yangtze river and its main stream. The results show that the low water level of Poyang Lake will exist for a long time in low-water season, and the impact on Poyang Lake will continue to deteriorate. It is proposed that the construction of Poyang Lake Water Conservancy Project is the best measure to solve the problem of low water level in low-water season.