Abstract:Availability is the most important index for evaluation of repairable system for users, and the dynamic availability level is determined by the coupling of reliability and maintainability. The dynamic availability as the core, the inner link of failure (reliability), repair rate(maintainability) and mutual influence and couplings of availability for repairable system were studied, instantaneous availability model, steady state availability model and average availability model in specified time interval for repairable system were built, and a set of usability dynamic mode was formed. Combining with the analysis for some series of availability of CNC machine, dynamic analysis can describe dynamic change of the process of availability in different time effectively, and it is an important guiding significance for the prediction of reliability and maintainability for the system.