Impulsive wave pressures due to breaking waves and overtopping waves are often much larger than usualwave forces. They can be predicted by experimental formulae for practical use. Because the xperimentalresults are greatly dependent on the structural condition and the wave profile, it is desirable that theimpulsive wave pressure should be predicted by numerical simulations.
　The problem of the numerical wave pressures simulation is the occurrence of the huge numerical error,called Spike Noise. Since the characteristics of the Spike Noise are similar to that of the impulsive wavepressures, it is difficult to remove the Spike Noise appropriately.
　Therefore the objectives of this paper are first to clarify the mechanism of the Spike Noise using theCADMAS-SURF program, which is the program for the maritime structural design with VOF method, nextto remove the Spike Noise by modifying the numerical scheme, and to verify this model by the comparisonwith experimental data of the wave pressures acting on the vertical breakwater and the pressures acting onthe structure behind the seawall.
　Conclusions of this paper are following:
　1. The developed model can be applied to the impulsive wave pressures acting on the vertical wall due tobreaking waves.
　2. The hydraulic pressures acting on the structure behind seawall due to overtopping waves and the watermass after attacking the wall also can be predicted by this model.
　3. In the area suffered from flooded water due to Typhoon, the difference of local damage levels, which iscaused by the difference of the cross section and wave condition in front of the seawall, could bereproduced numerically.