This paper gives one method to estimate the structural response of ship structures under water impact pressure. A series of drop tests of a cylinder with diameter of 312 mm is carried out to measure water impact pressures and strains on the surface of a cylinder. Numerical analyses are carried out for one of the drop tests to reproduce the structural response under measured time history of pressures. In spite of the existance of large local vibrations shown in the numerically estimated strain values, the numerically estimated strain values and the measured values show the same tendency on the whole. This result shows the numericaI method, we employed here, can be used for this purpose. Then we tried to evaluate the effects of maximum impact pressure on the maximum strain value. Two kinds of pressure histograms are used to estimate the maximum strain values. The strain values obtained from the pressure histogram with maximum impact pressure show less effects than that without maximum impact pressure. Finally, we modified the maximum impact pressure value of the measured time history of pressures to be used for numerical analysis. One is with the value of twice as much as measured value and the other is with the mean value of before and after the peak value. The results show that the maximum impact pressure value itself has little effects on the maximum strain value, while the time integration of pressure seems to have more effects than that of maximum impact pressure.