As it possesses characteristics such as high concurrency, high scalability, high cost-effectiveness and so on, the RAID system is the current solution is one of the main technology of information system external storage. With the popularity of the applications of the technology as well as the expansion of the system size, its failure increases dramatically, so the research on the reliability of RAID system has become a hot spot. Based on the reliability analysis of RAID system, the reliability mathematical model was derived.