Abstract: The storage capacity of Poyang Lake is influenced by the flow from the main stream of the Yangtze River and five rivers in the Poyang Lake basin. After the Three Gorges Dam (TGD) went into operation,hydrological changes in the main stream of the Yangtze River impacted water exchange between the river and Poyang Lake. Based on the analysis of measured data and factors influencing outflow at Hukou station,empirical formulas describing outflow at Hukou station and critical water level for lake storage capacity was established. The change in lake storage capacity in the months before and after the construction of the TGD was then analyzed quantitatively. The results show that the flows from the main stream of the Yangtze River and the five rivers in the Poyang Lake basin affected outflow and water storage capacity by changing the water level difference between Xingzi and Hukou stations and by changing the water level at Hukou station. But the Yangtze River and the five rivers in Poyang Lake basin dirrered in process and degree. Given no change in the water level at Hukou station,when the flow from the lake basin increased by 1 000 m³/s,the outflow increased by 304 m³/s. When the flow from the main stream of the Yangtze River increased by 1 000 m³/s,the outflow decreased by 723 m³/s. In addition,the TGD already had an impact on the water storage capacity of Poyang Lake. The water volume of Poyang Lake decreased 49.4% in September,but increased 47.7% in May.