With the rapid progress of science and technology, difficult-to-machine materials and parts with special-shaped surfaces have been widely used, and traditional cutting techniques are difficult (or unable) to solve the emerging processing problems. Special processing methods such as ultrasonic, laser, electrical discharge and electrochemical machining can effectively solve technical problems. Each single processing technology has its own advantages, but also has its limitations. For example, cutting high-hardness materials is difficult. Ultrasonic machining is only effective for hard and brittle materials. The overall efficiency of electrical discharge machining (EDM) and wire-cutting is relatively low, and there is a surface deterioration layer. The accuracy of conventional-parameter electrochemical machining is not high enough, and there are environmental protection issues. In practice, the multi-energy field processing method has the advantage of multi-technology compounding. This paper systematically analyzes and reviews the mechanism and application status of multi-energy field processing such as ultrasonicassisted cutting, ultrasonic-assisted laser, ultrasonic–compounded electrical discharge, ultrasonic–compounded electrochemical machining and ultrasonic–compounded mechanical–electrochemical–electrical discharge. Ultrasonic-assisted cutting can significantly reduce the cutting force and heat, improve chip evacuation conditions, minimize (or avoid) surface defects, and effectively enhance machining accuracy and efficiency. Ultrasonic-assisted laser processing can effectively solve the problems of product removal and surface quality. Ultrasonic–compounded electrical discharge machining not only ensures machining accuracy but also significantly enhances machining efficiency. In addition, the polishing effect of ultrasound can improve the surface quality of electrical discharge processing. The ultrasonic effect can enhance and improve the effect  of the electrochemical inter-electrode action and increase the nonlinearity of the electrochemical material removal. The ultrasonic-compounded electrochemical machining can significantly improve the processing accuracy. The multi-energy field machining methods of ultrasonic-compounded mechanical–electrochemical–electrical discharge have the interaction of parameters that can “retain the advantages and eliminate the disadvantages”, have the advantage of multi-technology compounding. Through the optimization and coordination of the parameters of the multi-energy field, the difficult-toprocess parts of different performance materials can be optimized. The paper systematically summarizes the characteristics, technical indicators and practical applications of ultrasonic – compounded mechanical–electrochemical–electrical discharge multi-energy field machining, analyzes the existing problems, discusses the effective solutions, and analyzes and prospects the relevant research work in the future.