In this study, a two-dimensional numerical method based on the volume of fluid method is used to solve for water sloshing. The 2D equations of fluid motion are derived in a moving coordinate system. For modeling impact pressure induced by large amplitude sloshing, an emphasis is given to the numerical treatment of the free surface, which is sensitive to the simulation. Liquid sloshing inside a rectangular tank is simulated. The time histories of the free surface shape and the dynamic pressure inside the tank are obtained. The results are compared with an experimental data. These comparisons show that this method can be used to simulate the sloshing induced impact loads. Then series of violent sloshing phenomenon is given and compared.