Abstract: The failure mode of ship structure attacked by typical semi-armour-piercing missile in target practice experiment was analyzed. The characters of internal explosion load and the failure mode of gross panel of the cabin were studied by numerical simulation. Results show that the explosion loads and the failure modes of the gross panel under explosion inside a cabin have many differences from under explosion in an open area; the dynamic response of the gross panel under explosion inside a cabin can not be simulated under explosion in an open area; the explosion loads acting on the gross panel inside a cabin, include reflected shock wave, converged shock wave on the corner, and the quasi-static pressure. Intensities of converged shock wave on the corners of two gross panels and three gross panels are 5 and 12 times larger than that of the reflected shock wave respectively. The gross panels of a cabin have 4 failure modes, under internal explosion loads, in which mode Ⅲ and Ⅳ are most frequent. The stiffeners of the panels placed on the blast side can enhance the local damage, but can weaken the converged shock wave on the corner, and decrease the tearing damage on the corner.