The grinding wheel system is the main function system of CNC forming gear grinding machine determining the precision and quality of processing. In order to improve its reliability, it is necessary to find the failure cause and weak link of the grinding wheel system. The grinding wheel system failure was taken as the top event for FTA analysis, then AHP was used to build a fault hierarchy model, the probability weight value of each failure factor was calculated, the key failure factors that affected the grinding wheel system were clarified, and the improvement measures were proposed finally to improve the reliability of the grinding wheel system.