Abstract: Underwater explosion tests were performed beneath the clamped square plates using 2.5 g TNT, RDX, and B explosive. The dynamic responses of the plate were investigated under the joint actions of underwater explosive shock wave, bubble pulsation, and water jet load. The results show that: lower energy TNT causes permanent convex deformation integrally on the square plate, whereas higher energy explosives B and RDX cause permanent convex deformations on the middle-upper side and a concave deformation on the plate’s edge. To further investigate the damage characteristics of clamped square plate caused by different explosives, numerical simulation was performed using Abaqus. The results show that: during the process of bubble’s expansion, its internal pressure gradually drops to a lower level than the atmosphere pressure, resulting in a pressure difference and concave deformation of the plate. The steel plate then rebounds as a result of the combined action of bubble pulsation and water jet. Different explosives show different bubble effect during the process of plate rebounding, which is the primary reason for the various damage forms. Increasing the plate thickness effectively prevents the clamped square plate’s middle convex side concave deformation. This work can be employed to design underwater warheads.