This paper analyzes the wave pressure on the sea face of the longitudinal beam and the horizontal force of the upper structure through the physical model test. It points out dominant factors which influence the horizontal force of the superstructure, such as wave height H, longitudinal beam height R, overheight Δh, wave period T, as well as the number of longitudinal beams n affected by the single wave crest. The formulas of wave horizontal force are fitted by the actor analysis method, and the calculated values are compared with the trial values.