The automatic tool changer system is the key functional unit of the machining center, which reliability directly affects overall of that of the machining center. Therefore, its reliability research has important research value in improving the reliability of the machining center. According to the automatic tool changer system produced by the foreign highgrade machining center, traditional frequency method and mathematical statistics were applied separately. Failure mode analysis results and the mean failure frequency were calculated. Based on it, the mean time between failures (MTBF), mean time to first failure (MTTFF) and other multiple reliability indexes are acquired by mathematics modeling.