Abstract: The extension set theory is used to construct a matter-element model for the reliability evaluation of CNC machine tools.The correlation function of the extension set theory is used to obtain the reliability level correlation degree of each evaluation index, the AHP-entropy weight method is introduced to determine the weight of each evaluation index in the matter-element model, and the comprehensive correlation degree of the reliability of the evaluation index is obtained.The membership degree selection principle determines the reliability evaluation level of machine tools.Taking the working status of a certain type of machining center abroad as the research object, using the expandable theory of AHP-entropy method to establish a reliability evaluation model, it is concluded that the reliability level of the spindle system and the feed system of this type of machining center are both "good".