Model tests on impulsive water pressures acting on the bottom of a high-speed boat in waves were carried out including in the case of flying motion over the wave surface. The result was compared with that of the ship tests in seas and a good agreement was shown. Impulsive water pressures measured by the model tests were analysed by Stavovy and Chuang's method. As the result, it was made clear that the impulsive water pressures acting on the bottom of the high-speed boat can be estimated by Stavovy and Chuang's method, if only the motions in waves can be simulated exactly.