Abstract: The power ultrasonic machining of CNC machine tools can effectively reduce the cutting force by superimposing high-frequency axial ultrasonic vibration on the rotating tool. It is suitable for processing all kinds of special materials. The traditional ultrasonic machining system is usually powered by a contact slip ring, which has disadvantages such as easy wear of the brush and poor interchangeability. By designing a wireless power supply device based on a non-contact transformer and a compensation circuit on the primary and secondary sides of the transformer, and using Maxwell software to carry on electromagnetic simulation to it. The influence of the air gap on the transmission efficiency is studied, and the performance of the CNC machining system is finally verified by experiments. The results show that the power transmission efficiency decreases with the increase of the air gap, and the compensation circuit design can effectively improve the vibration performance of the ultrasonic machining tool of the CNC machine tool.