Abstract: In a core-melt nuclear reactor accident, the important phenomenon, the interaction between molten fuel and residual water, is difficult to simulate numerically. In the present study, MPS（Moving Particle Semi-implicit Method） is employed to simulate the molten fuel ball impacting liquid pool and its fragmentation behaviors during falling into the water pool and in the water tank. The simulation results indicate that during the impacting process, the molten fuel ball becomes flat and Rayleigh-Tayor instability occurred and the boundary layer stripped. In the initial phase, its velocity rapidly decreased about 15%. The results showed a good agreement with the picture observed in experiments, which verified the rationality of molten fuel behavior simulated using MPS.