Abstract: To further clarify the impact of construction of the Three Gorges Reservoir on its tributaries,a three-dimensional hydrodynamic model of Changshou-Fuling section of Yangtze River was developed based on EFDC.Then an analysis of the hydrodynamics and the long term mass transport behaviors under backwater effect in the Taohuaxi River and Longxi River was presented.There followed Lagrangian particle tracing method to analyze pollutant trajectories of different positions in main streams and tributaries.The results show that trunk river backwater played a significant role in branch river during low-water period.And distinct circulation was shown in branch rivers estuary.However,in high-water period,estuarine circulation area in Longxi river decreased and disappeared,while the one in Taohuaxi river was still evident.Different inputaction from main streams to tributaries was discovered.