This paper investigates the performance of deteriorating systems maintained under structural constraints using a simulation approach. Three maintenance polices are investigated, and the performance of the system is measured by the steady-state system availability. The best maintenance policy is chosen with the highest steady-state availability. Unlike those widely used methods that treat such systems as continuous-time Markov processes, the proposed simulation model is able to deal with more general failure time and repair time distributions. Moreover, since desirable performance indices can be easily obtained using this method, it will be an effective tool to assist in selecting the optimal maintenance policy for a complex system.