This paper proposes a method based on extended reachability matrix combined with component design for the AGENT to build the model of aircraft systems in maintenance simulation process. It can not only solve the problem of expression of logic relationship between the LRUs, but also can provide the system with redundancy. The method can describe the component's work logic in the system and the effect of component state change on the system. The logic of aircraft system can be abstracted and transformed into the effable object of computer with this method. Through the analysis of the reachable matrix, The behavior of the signal transmission and the behavior of the service can be defined. At Last, the feasibility of the method is verified by constructing an automatic flight system (AFS).