Rotary ultrasonic vibration-assisted EDM is a composite machining method which uses EDM technology to process metal surface and adds rotation and ultrasonic vibration. In this paper, the failure rate of each module of the rotary ultrasonic vibration-assisted EDM machine tool can be accurately predicted by the maximum entropy ordered weighted average algorithm so that the corrected maintenance cost can be predicted. And effective control of preventive maintenance costs can be achieved by selecting the best maintenance times under the premise of reliability. The results showed that the reliability of rotary ultrasonic vibration-assisted EDM machine tool is smoother at non-fixed maintenance intervals by varying the maintenance interval according to the comparison between non-fixed and fixed maintenance cycle. The cost of corrective maintenance can be reduced by varying the measurement to achieve cost optimization in the context of reliability with an optimum number of maintenance cycles and reliability.