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.