Abstract: The change of the water level discharge relationship of the hydrometric station reflects the interaction between rivers and lakes. In order to explore the interaction between the Yangtze River and Poyang Lake after the operation of the Long Three Gorges Project, the water level and flow relationship between Jiujiang Station and Hukou Station are analyzed. Based on the water level and discharge relationship considering the backwater jacking effect, the calculation method of water level and flow in Jiujiang and Hukou is established. The research shows that after the Three Gorges Project is put into operation, the water level and flow curve of Jiujiang Station moves down, the average water level for many years is 0.8 m lower than that before the Three Gorges Reservoir is built. The low water level area of the comprehensive line also moves down year by year, and the average water level of Hukou Station decreases by 0.7 m due to the reduction of Jiujiang water level.The influence range of the Three Gorges Project on the main stream of the Yangtze River is above Datong, and the jacking effect of the Yangtze River on Poyang Lake decreases by 1.1%. Based on previous studies, the calculation method of Hukou flow is proposed. The accuracy of the calculation formula of data fitting from 2003 to 2021 reaches 86%. And the relationship curve of water level and flow is established. The discrimination relationship of lake mouth backflow is proposed. When the difference between the flow of Jiujiang River and the flow of Wuhe River exceeds 30 000 m3/s, the Yangtze River water may backflow into Poyang Lake. The research results provide some reference for the analysis of the jacking relationship between the Yangtze River and Poyang Lake.