Considering material strength of the outside plate of a ship,a numerical model of underwater contact explosion is built based on SPH method.Mixed density and generalized smooth length are put forward to overcome calculation breakdown in numerical simulations.Underwater contact explosion of ships is simulated,and calculation results agree well with shock wave theory and contact explosion tests.It shows that a circular extrusion crevasse,whose size is close to the thickness of the explosive,forms on the steel structure in contact explosion.As regularizing thickness of the steel plate and the explosive reaches 1.8,only plastic deformation occurs on the plate.Reflection coefficient of the steel,which equals about 1.2,and approximate deformation formulas are obtaind.