Mixed powder electric discharge machining（EDM）is a new machining process,by adding fine powder to the working fluid,it can significantly improves the surface roughness of the workpiece. The formation of surface roughness of EDM is directly related to the size of the discharge pit, while the size of the discharge pit is closely related to the temperature field of the single pulse discharge. In order to further improve the surface quality of the mixed powder processing, the temperature field of the discharge point was simulated and analyzed by using ANSYS, and the distribution law of the surface temperature field of the workpiece was obtained. The material removal mechanism was revealed, and the relationship between the surface roughness and the temperature field was clarified. It provides a theoretical basis for predicting and improving the surface quality of mixed powder processing and practical application.