Poyang Lake is China's biggest freshwater lake, its water level changes, which will have a very important and far-reaching influence to the social, economic, and environmental of the area. Meanwhile, we analyzed the water change factors from five aspects of Poyang Lake, the five rivers of Poyang Lake basin precipitation, jacking of Yangtze River main stream flowing effect, Poyang Lake itself for the carrying capacity of water and artificial sand mining. We find Nanchang rainfall and water level of Poyang Lake has evident consistency, and this consistency is becoming more and more obvious after 2000. Yangtze River jacking flowing makes the water level of Poyang Lake appears certain rise, and the height of the water level depends on the middle and lower reaches of the Yangtze River and Poyang Lake exports out of the water level, flow and etc. In addition, we also found that the lake itself on the bearing capacity of the water.