The reliability of ship structure subjected to inner explosion is important both in theory and in practice. In this paper, the destroy probability of general structure ships and box girder structure ships are calculated, with random variables taken into consideration. Then the effect of box girder structure in improving structural reliability is analyzed based on comparison. The Monte-Carlo Method combined with the Maximum Entropy Method is used in this paper. Simulations of structural responses of the ship subjected to cabin inner explosion are done by MSC-Dytran, taking the fluid-structure-interaction into consideration. The results indicate that the box girder structure can significantly reduce the deformation of the 01 deck under inner explosion longitudinally and transversally.