Abstract: A predictable hydrodynamic model was established to evaluate the impact of the Three Gorges Reservoir on hydrodynamics along the tidal reach of the Yangtze River. With merely upstream discharge boundary condition, the model was able to provide the downstream boundary condition considering interaction between the river runoff and the ocean tide. Quantitative analysis was achieved with 10-year continuous simulations of a one-dimensional (1D) unsteady numerical model of channel network in tidal reach of the Yangtze River from Datong to Xuliujing before and after the impoundment of the Three Gorges Reservoir. Statistical result indicates that runoff regulation of the reservoir plays an important role in both cumulative frequencies of tidal level and seasonal hydrodynamic processes.