According to standard IV fragment-proof grading requirements of GJB 4300-2002 Army Bullet-Proof Vest Safety Technology Requirement, use numerical simulation method to study the bullet-proof performance of ceramic/ steel targets. The initial velocity was set, and then through changing thickness of two materials, the entire bullet-proof performance of different states was confirmed. The results of simulation showed that, when the thickness of ceramic plate was large, the bullet-proof performance was effect slightly by steel plate. Then the thickness of steel plate can be selected following the demand of maximum deforming. The conclusion is that, if the demand of standard IV in GJB 4300-2002 could be met, the thickness of ceramic plate must be above 12mm. The results are useful to engineering application.