A 2D numerical model is built to simulate the sediment transport process in the Yangtze estuary by DELFT3D model at first. Then a morphological model is built with generalized flux process in the flood and dry seasons combined with the variation of tidal ranges at outer sea for a long-period simulation of the evolution of tidal flat. The model is validated through the surveyed data and the simulation result presents a good agreement with the real measured value. Further-more, a prediction of the evolution process of Nanhui tidal flat is given under the impact of the Three Gorges Project. In general, there’s still a stable development of Nanhui tidal flat and expanding to the southeast with no significant erosion caused by the reduction of water-sediment from the upstream in the next 5 to 20 years after the Three Gorge reservoir’s operation.