Abstract: A two-dimensional numerical model was selected for the proposed inland nuclear power plant in this paper. The two-dimensional hydrodynamic model of the Yangtze River estuary was constructed based on the MIKE model. The flow field of receiving water and the diffusion of radioactive liquid effluent in the Yangtze River delta under a hypothetical accident were simulated. The detention time, process and extent of radioactive contamination in the Yangtze River delta under tidal action were evaluated. The simulation results show that it could basically reflect the actual situation of receiving water. Tidal action will increase the detention time of nuclides in delta waters, but it will also bring radionuclides to the outer sea, and the nuclide concentration will gradually decrease.