To explore the hydrodynamic environment and sediment scouring and silting around the Yangtze estuary before and after the construction of the Qingcaosha Reservoir Project, a depth-averaged 2D tidal current and suspended sediment numerical model was established to simulate erosion and deposition. Combined with a modified empirical formula proposed by Wang Yigang, the numerical model can simulate the intensity of erosion and deposition simultaneously. The calculated results show that, after the construction of the reservoir, the diversion ratio and flow velocity in the north channel of the Changing Island decrease but increase in the south channel. The south channel of the reservoir shows a scouring state, while deposition dominates in the north channel. The variation in the south channel is less than that in the north channel, indicating that the construction of the reservoir project has a greater impact on the underwater topography in the north channel. The calculated results by the modified Wang Yigang’s formula are in good agreement with the measured topography and the numerical results after the project construction.