By taking both CMF (Common Mode Failure) and middle states into account, numerical analysis of availability of cluster system is analyzed. Firstly, a CTMC (Continuous Time Markov Chain) model of cluster system containing three cluster nodes is constructed with failure rate (λ), repair rate (μ), CMF rate (7), reconfiguration rate (β) and reset rate (á) etc. Then the steady state solution of the CMTC model is concerned by solving the equations with the combination of several parameters. Subsequently, the effect of probability of being in automatic recovery mode (k) on availability of cluster system is analyzed and discussed via numerical values-based chart thereby. This work offers quantitative analysis of cluster system's availability.