This report is concerned with the elasto-plastic response of the bottom plate of aluminum high speed crafts due to slamming pressure which sometimes causes damages among rough seas. Drop test of full-scale model of the bottom plate on the water surface is carried out and experimental values are compared with theoretical results. At first, measured data are analyzed within frequency domain in order to get the linearity between water pressure and dynamic response. Then, assuming the damping effect caused by the air layer between the water surface and the plate, the dynamic response of the bottom plate is numerically calculated by using the finite strip method. It is shown that experimental values are agree well with the theoretical results, by choosing reasonable damping factor.