Based on analysis of characteristic and engagement process on low layer missile defense battle, the paper discusses the essence of engagement action and the key models on low layer missile defense battle using system theory and military operations research method. 从低层反导作战特点和反导交战行动(EO)过程入手,用系统的观点和军事运筹方法对低层反导作战交战行动(EO)的本质和关键模型进行了研究;