<p>A theoretical analysis method was developed for the study of impact loads on wedge-prism bodies during water entry. By employing the slicing concept, it extends the two-dimensional water entry theory into three dimensions, while also considering the downwash momentum. The motion equations account for movement parallel to the keel direction. The effectiveness of the three-dimensional theory was validated by comparing it with experimental results, demonstrating that the method can rapidly and accurately calculate the water impact loads on wedge-prism bodies. Using this theory, the impact loads of wedge-prism bodies at various deadrise angles and trim angles are calculated. The computational accuracy of various two-dimensional wedge added mass forms is compared, and the variation pattern of impact acceleration is obtained. This can provide a reference for the configuration and motion parameter design of structures.</p>