Abstract: The underwater vertical launch of submarine-launched ballistic weapons is a critical technology in the sea-based strategic deterrence system. During the water-exit phase, the vehicle faces complex multiphase hydrodynamic challenges that directly affect its load characteristics and ballistic stability. In a wave environment, disturbances of wave surface particles further complicate cavitation evolution and dynamic response processes. This study, based on fifth-order Stokes wave theory, integrates the large eddy simulation (LES), the volume of fluid (VOF) multiphase flow model, and the Schnerr-Sauer cavitation model. By employing boundary wave-making and overset grid techniques, a high-fidelity numerical simulation model is developed to investigate the water-exit behavior of underwater vehicles under wave conditions. The study systematically explores the influence of wave-induced effects on cavitation field evolution, collapse-induced loads, and vehicle motion attitude. The results reveal that under still water conditions, the cavitation growth, shedding, and collapse processes on both sides of the vehicle are highly symmetric, generating a pair of narrow pulse-width, high-magnitude, and oppositely directed lateral loads during water exit. In wave environments, asymmetric flows induced by wave crest and trough phases significantly alter the cavitation structure: under the crest phase, the right-side cavity is larger than the left, while the opposite is observed under the trough phase. The collapse load on the larger cavity side is considerably higher than that on the opposite side and exhibits a notable time lag. Furthermore, the vehicle trajectory and deflection angle deviate significantly under crest and trough phases, with opposite deflection directions. In contrast, the motion characteristics during pre-crest and post-crest phases resemble those in still water, exhibiting smaller deviations. In twin-body launch scenarios, wave disturbances and inter-body flow field interference jointly influence the dynamics: the twin bodies shift to the right under the crest phase and to the left under the trough phase. The lateral displacement is mainly driven by wave-induced disturbances, whereas the deflection attitude is primarily governed by flow field interactions.