Abstract: A new analysis method is proposed for studying the reliability of a repairable CIMS with finite buffers. These buffers lead to blockage and starvation in the transfer lines and is very difficult to solve in a system. By means of queueing theory of Markov process, we analyze the intermediate buffer, equivalent workstation and system reliability in steps. From the principle of equilibrium, a theorem of necessary and sufficient condition without loss of any working parts in the transfer lines is given, which can help us' to solve the problem and obtain the accurate result. Finally, two examples are given for illustrating the application of this method.