TPNSim++ is the object-oriented framework for the discrete event simulation of military systems, developed by authors. The simulation world view of TPNSim++ is on the basis of activity scanning. TPNSim++ is implemented as C++ class library under Windows 95/NT. It uses the extended timed Petri nets which are called TPNSim nets for simulation modeling tool. The aim of this study is to conduct a comparative study of TPNSim++ and SLAM II in the simulation of military maintenance systems for the validation and the applicability of TPNSim++. From this study, TPNSim++ and SLAMII have given the same results under the equivalent assumption. Thus we can get the validation of TPNSim++ and its applicability to the simulation of maintenance systems.