In this paper,the open or restricted water under the slamming by a flat-bottom structure is taken as the research object,and a computational fluid dynamics（CFD） technique is used to investigate the 3D hydrodynamic characteristics of the water.The investigation is conducted by using the volume of fluid（VOF） method and the dynamic mesh method,with the factors of open or restricted boundary conditions being considered.Moreover,the phenomena of multiple pressure peak values observed during the slamming simulation are analyzed,and the corresponding generation mechanisms are discussed.The comparison between the simulated and the experimental results indicate that the proposed numerical method helps to analyze the hydrodynamic characteristics reasonably,and that it can effectively simulate the wave-making and underwater pressure distribution variation agitated by the slamming of the flat-bottom structure on the open or restricted water with free surface.