It is difficult to make quantitative analysis to time efficiency of a system.This paper mainly focuses on the theoretic model of time Petri net.Based on the time equivalent transformation of Petri net model, models for the air defense combat based on the Military Information Service System (MISS) are established with the Petri net.Also, the equivalent delay of the whole operational process is derived.On this basis, analysis is made to the system time efficiency through simulation with Matlab, and the effectiveness of the method is verified.