System availability has a great importance in recent years due to the technological environment and operating costs. The performance of equipment usually depends on the availability of the equipment, operation process, maintenance strategy and etc. In this case, when the availability of a system is low, actions are needed to be taken to improve the availability of the system. One of way is by reducig the failure rate or increasing the repair rate of the equipment. The objective of this paper is to develop the availability model for repairable system, where it deals with availability optimization and evaluation of optimum availability for repairable system under study of an industrial centrifugal gas compressor.