In this paper, the elastoplastic response of copper, steel and aluminum circular plates with clamped boundary conditions subjected to underwater explosion loading is investigated. Cavitation is a phenomenon that can be occurred for plates in the process of underwater explosion forming. The total pressure of the explosion becomes zero at the cavitation time, so that the governing equations of motion time will be different before and fter the cavitation. As a result, in terms of analysis and design, the cavitation time is significant in studying the behavior of a circular plate at underwater explosive loading. By appling the energy method and based on Hamilton principle and variation method the equations of motion of an underwater circular plate subjected to explosive loading are derived. Then, in order to obtain the forced response of the circular plate, the exact free vibration solution is derived to calculate the mode shapes. Then, the velocity and generated stress of plate during cavitation time are calculated and compared with the yield stress plates. Using this method, one can distinguish the cavitation with in the elastic or plastic regimes. By recognizing the time of cavitation in the range of elastic or plastic, the displacement and velocity field of plate are determined in duration of explosive loading. Results show that the cavitation time is on the order of microsecond. Depending on amount of charge mass and stand-off, the cavitation time may be occurred in elastic or plastic regime.