Abstract: In order to assess the defensive performance of multi-layered blast protection blisters of large warships subjected to underwater contact explosion，both evaluation methods and procedures are suggested based on the principles of dynamics and energy. Basically，the capability of water blisters absorbing explosive blast is assessed according to the penetration properties of high velocity fragments in different media， and the impulse loads and contact explosion shock wave loads on the inner wall are analyzed. The theoretical protective efficacy of multi-layered defensive structures is validated by employing a typical ship cabin contact explosion model under 300 g TNT. The results indicate that the velocity of damaged fragment can be decreased to a safety speed through a length of 0.1 m，and the minimum critical thickness of the inside wall structure of water blisters is 3.8 mm.