Abstract: Objectives To investigate the coupling characteristics of blast waves and fragments generated by a warhead detonating inside a ship compartment under dynamic explosion conditions, and their effects on structural damage modes. Methods A fluid–structure interaction model was established, and the FEM-SPH method was used to simulate warhead fragmentation and fragment dispersion. The numerical method was validated against experimental data. Parametric analyses were conducted for different detonation positions and initial velocities, with damage evaluated by pressure response, fragment kinetic energy, structural deformation, and breach area. Results Compared with static detonation, dynamic detonation significantly altered the loading characteristics. Increasing initial velocity accelerated the rise of forward peak pressure while reducing the backward peak pressure. Fragment kinetic energy increased markedly with initial velocity and was mainly derived from the initial kinetic energy. The breach area ratio of the forward-facing outer plate increased from 3.11% to 18.14%. Conclusions Fragment-induced perforation promoted pressure venting and weakened corner pressure concentration, causing the dominant failure mode to shift from corner tearing to corner plastic deformation with mid-span tearing. Dynamic detonation more readily caused through-penetration and tearing propagation, with damage jointly governed by detonation position and initial velocity.