With the increased reliance on M & S(Modeling & Simulation) in military training, defense analysis, and system acquisition. The credibility of M & S becomes even more critical issue in the M & S application community. In this paper, we have introduced the VV & A(Verification, Validation and Accreditation) concept of M & S for the assurance of its credibility, and proposed the VV & A model applicable to a military simulator development with the illustrative example of MSAM(Medium range-Surface to Air Missile) system simulator.