Abstract: Based on the randomness of wave surface slope, the probability distribution of effective impact angle of bow fare impact was studied. The deadrise angle at the impact region of ship hull surface was expanded with Taylor series in the vertical normal plane, and the probability density function for the angle was derived on the basis of random characteristics of ship motion response. In terms of the theory of random ocean waves and Chuang’s analytical method of slamming pressures for vehicles, the probability density function for the effective impact angle was derived, providing basis for further study of the probability prediction method of bow flare impact.