A model test in regular waves was carried out in order to develop a method for estimating horizontal impact pressure which acts on the structures on deck due to shipping water. A model of a cargo ship for Japanese domestic voyage was used. The bow flare form and bow height were varied from the original one to investigate the effect of them on the horizontal impact pressure. It was found that the effect of bow flare form is small compared to the one of bow height. The theory of “flood waves” was applied for evaluating the shipping water height distribution on deck. The inputs of this method are relative water height at bow and pitching angle those can be calculated by strip theory and so forth. Having compared with measured data, it was confirmed that this theory can give a good estimation for the shipping water height distribution. The Wagner's theory of wave impact was applied for evaluating the horizontal impact pressure. Key quantities for the calculation, e.g. the angle between the front slope of shipping water and the structure, were evaluated by the theory of “flood waves”. Having compared with measured data, it was confirmed that the combination of these two methods is practical enough for estimating horizontal impact pressure on deck structures.