Abstract: Traditional WEDM use point-by-point comparison interpolation principle for processing. It has some disadvantages such as low efficiency, rough surface and other shortcomings. Aimed at these problems, true circular interpolation method is proposed. A new type of rotary workbench with three degrees of freedom, is added to the original two degrees of freedom(X direction, Y direction) WEDM workbench in order to change "point-by-point comparison interpolation" to "true circular interpolation". Working principle of true circular interpolation method and its realization method are discussed in detail. Example analyses show that, using the true circular interpolation method to process pure arc and 45-degree diagonal line, the efficiency is improved by 21.46%, 29.29%, respectively. And molybdenum wire walking trajectory is smooth arc and straight line, the surface quality of wire cutting parts is greatly improved. The mothed extends the application field of wire electric discharge cutting technology.