This paper studies the entity modeling method in Agent-based TBM combat simulation system. The architecture of the TBM combat simulation by using HLA/RTI platform has been build. According to the command hierarchy features of military operations, Agent entities are divided into three levels, and a semi-autonomous Agent model has been build. We present a Semantic-based multiple-layered military scenario development framework and implement a Semantic-based Military Scenario Development platform, which can support military commander to semi-automatically generate a military mission plan with MSDL document. Finally gives the flow chart of TBM combat simulation system.