This study aimed to investigate the forces of a high-speed catamaran under the action of regular head waves at speed of 20 kn, and provided data support for the structural design of high-speed catamarans. This paper employs Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) methods to construct a unidirectional fluid-structure interaction (FSI) numerical model for a high-speed hull with an aluminum alloy shell material, based on the Reynolds-averaged Navier–Stokes (RANS) equations. Structural dynamic analysis is performed using the numerical results, focusing on the study of the hull’s structural forces and deformation characteristics under head wave regular wave conditions. By adjusting the local structure of the hull frame, a high-speed vessel design and optimization were achieved in accordance with regulatory requirements. The results show that the maximum equivalent stress and maximum shear stress both were occurred when the wavelength-to-ship-length ratio was approximately 1.25. The maximum stress was occurred at the wavelength from 14 to 16 m. The maximum deformation was 3 mm at the bow of longitudinal girder under the wave load. The maximum equivalent stress and shear stress were typically at the bow of ship bottom. Through appropriate structural reinforcement, the equivalent stress could be significantly reduced, thereby improving the structural strength.