Abstract: Aiming at the discharging of liquid effluent from coastal nuclear facilities in the sea area, this paper uses the hydrodynamic software MIKE21 to establish the hydrodynamic and diffusion model of the sea area, simulates the dilution and diffusion of the radionuclides in the liquid effluent under the action of tides, and studies the influence of factors such as type, tide level and discharge period on the effect of radionuclide dilution and diffusion.Simulation studies have found that intensively discharging the liquid effluents during the ebb period when the tidal range is large, the concentration of radionuclides near the shore is lower, which is more conducive to the diffusion of liquid effluents to the open sea.Based on the simulation results, this paper also proposes an optimization scheme for the discharge of liquid effluent from nuclear facilities, and evaluates the radiation environmental impact of the plan, which provides a certain reference value for engineering applications.