Antimissile situation assessment(SA) has important significance of antimissile operational command. In order to further study and optimize the antimissile SA process, in this paper, the process of antimissile was first analyzed and SA reasoning model was built in three phases: Then missile model and single-time SA model were built based on Petri net, and the global SA process model was further built; Finally, the global model was simulated utilizing VisObjNet software and Matlab software from the data stream level and reasoning level, and the effectiveness of the model was validated. The model can provide better decision support for antimissile combat command.