Abstract: Three Gorges Project has been running for more than ten years. According to the statistical data of Datong Hydrometric station, the average maximum flow in flood season has been reduced by 8.4%, and the annual runoff has been reduced by about 5% since the impoundment of Three Gorges reservoir. According to the data of Nanjing tide station, the highest annual average water level has been reduced by 12cm since the impoundment, so the relative decrease of water level is obviously smaller than that of flow reduction, demonstrating that the relationship between water level and flow at high discharge at Nanjing hangs upside down. Based on the statistical analysis and correlation analysis of the daily average maximum water levels, daily maximum flows and annual runoffs of Nanjing tide station since 1950, we find that Nanjing tide station water level increases generally when level is higher than river beach elevation, and the amplitude is 2.65cm. The flow and runoff data of Nanjing tide station are the synchronous data of Datong hydrological station plus the lateral inflow. The results can provide basis for flood control and water resources development and utilization in Nanjing.