Abstract: In order to study the diffusion of airborne nuclides in marine environment after a nuclear accident, this paper took the island nuclear power plant as the research object, and simulated the underlying surface elements, wind speed changes and nozzle velocity changes of the island nuclear power plant by using computational fluid dynamics (CFD) simulation method, and verified the accuracy of CFD simulation by wind tunnel experiments. The results show that the mountain around the nuclear power plant has a significant effect on the maximum ground diffusion factor. When the height of the platform increases, the maximum ground diffusion factor decreases, which is closer to the nozzle. The increasing of the wind speed will cause the position of the maximum ground diffusion factor to shift back. As the nozzle velocity increases, the maximum diffusion factor on the ground becomes smaller and its position shifts back. Under the condition that the velocity of the nozzle changes, the CFD simulation value of the ground maximum diffusion factor has a multiple relationship with the calculated value of the Gaussian plume model.