Abstract: Based on monitoring and investigation of the inlake pollution loads and simultaneous monitoring of flow field & water quality under different hydrological conditions, the characteristics on distribution, transfer and reduction of nitrogen and phosphorus in Poyang Lake are studied using mathematical statistics. The results show that: (1) the TP and TN are the main pollutants which affect the water quality in Poyang Lake, and there is a close positive correlation between the pollution load and the inlake flow. (2) the TP and TN contaminants are not mix well in the lake, due to that the water exchange cycle is short. Nitrogen and phosphorus pollutants gradually transfer and diffuse to the downstream with the flow. (3) the water environment under lake state is better than that under the river state. The TP and TP generally do not simultaneously exceed the water quality standard in large area under the lakes state. (4) The water environment in Poyang Lake barely maintains the class Ⅲ standard. However, human activities have great potential to deteriorate the water environment. Finally, the countermeasures to protect the water environment quality in Poyang Lake are proposed based on the above conclusions.