For solving the problem of discontinuous factors (such as target crack), that resulting in large amount of calculation and low precision of finite element method, design the extended finite element method procedure through combination of the extended finite element method and level set theory. Based on experiment about projectile penetrates the target, adopt index discontinuous function to show the influence of crack on displacement, use level set theory to define the zero level set function which dimension is higher than interface to express crack interface, build models and carry on numerical calculate. The result shows this method can analysis crack growth accurately, and it can create the pictures of projectile penetrates the target and plastic strain in different stage