A numerical model for simulating unsteady flow and sediment transport in the mainstream and its tributaries of the Three Gorges Reservoir (TGR) area was presented in this paper. More tributaries could be included in the calculation with this tree-like rivernetwork model. The validity of the model was checked with the observed water and sediment data of the TGR from June 2003 to December 2009. Good agreement between the calculated results and the observed data indicated  this model could be used to simulate the flow and sediment transport in the TGR area, and hence could be applied to the modeling and prediction for the optimal operation of the TGR in the future.