ABSTRACT: The particle method (Moving Particle Semi-implicit method) is applied to violent free surface problems on marine engineering. The sloshing on very shallow depth condition and the very large motion of floating body with water invasion in waves are simulated successfully with it. These results show realistic behavior. INTRODUCTION After recent tragic losses of ships, many researchers have studied about the ship's damage stability and deck wetness. In these studies, they have always pointed out that behavior of water on the deck is very important. However violent free surface flow and dynamic effect of flow have hardly been considered. Almost studies of damage stability are stand on the quasi-static assumption about the behavior of water motion on the inner deck of ships. The deck wetness and the green water load acting on the structure have been treated with model experiments. In spite of an increase of computational resources in recent years, there has hardly been direct numerical simulation of these phenomena with CFD(Computational Fluid Dynamics) techniques. The reason of this exists as a difficulty in handling the violent free surface flow like fragmentation of fluid. Then VOF(Volume of Fluid Method) and its refined methods which use space fixed grid system has been used in several past studies. These methods are effective in handling violent free surface flow, but they include some of problems like numerical diffusion of free surface, stair effect, robustness of calculation and so on. Another difficulties of numerical simulation about problems exist in handling very large motion of boundary like the capsized hull. BEM(Boundary Element Method) with ALE(Arbitrary Lagrangian and Eulerian) grid has been used in researches of the numerical wave tank to simulate motion of floating body. However it is difficult to handle breaking waves, damaged hull's opening, etc. even if using ALE grid.