In order to study the dynamic diffusion mechanism and accident risk of tritium, a virtual simulation system for tritium diffusion based on the 3D graphics engine is developed. The accident simulation object is determined by the preliminary hazard analysis method for tritium system. The particle system is applied to simulate the dynamic process of the tritium diffusion, and the human-computer interaction function is realized based on virtual roaming and simulation technology. Finally, take the Tritium extraction system in the International Thermal nuclear Experimental Reactor (ITER) as an example, the dynamic diffusion process and concentration change of tritium is simulated when the hydrogen isotope separation column and pipeline leak. The simulation results provide a basis for the development of safety protection measures when tritium leaks.