A numerical model for simulating 1-D unsteady flow and sediment transport in the mainstream and its tributaries of the Three Gorges Reservoir (TGR) area was presented in this paper, and a three-gradation method was applied to solve the flow governing equation. The validity of the model was checked with the observed data of the TGR from June 2003 to December 2004. The calculated result was in good agreement with observed data. The model was further applied to predict the sedimentation process in the TGR in a 100year period with the discharge and sediment data of 1961 to 1970 series and under the normal water level operation condition. And the calculation results are reasonable. The simulated results show that this model could be used to simulate the discharge and sediment transport at the TGR.