This paper examines the performance of composite plates with PVC foam cores and T700/epoxy composites face sheets, and steel plate have the same areal mass when subjected to Underwater Explosion (UNDEX). The objective of this study is to evaluate the dynamic response of those plates. A non-linear dynamic numerical analysis of the underwater explosion phenomena is performed using the ABAQUS/Explicit finite element code, which provides an important analysis tool that can help engineers and designers to design and construct better structures to resist shock loads. The temporal evolutions of plate deflection and central deflection histories were obtained. Further investigations have been performed to study the behavior of failure. The results indicate that the behavior of composite plate with PVC foam core to resist shock loads resulting from an UNDEX is better than steel plate, and the core thickness has a great effect on the plate`s response. The obtained numerical results can help to suggest design guidelines of floating structures to enhance resistance to
underwater shock damage, since explosive tests are costly and dangerous.