Abstract: For the problem on three-dimensional numerical simulation of explosion in water, a method based on finite difference, which combines Lagrangian method and Eulerian method, is proposed. Control equations were transformed into discrete and difference forms in rectangle nets. To calculate the transported quantity, Eulerian step and fuzzy interface method were introduced to describe materials interface. The numerical simulation method was programmed and applied to three-dimensional numerical simulation of explosion in water in environment with rigid boundary. The results of simulation are consistent with actual explosion, especially the simulation result of diffusion of blast wave in water is better. It proves that the proposed numerical method is correct and effective.