A theoretical model of temperature for electrical discharge machining (EDM) is established. Based on finite element method, the distribution temperature fields of ZL108, YG15 and 45 carbon steel during EDM process are simulated with the aid of ANSYS software. The simulation model provides good effects on the surface quality forecast, parameter regulation and optimization in the process of EDM. Under same experimental conditions, the machining efficiencies of EDM ZL108, YG15 and 45 carbon steel are listed. The machining efficiency of EDM ZL108 or 45 carbon steel is much higher than YG15. The observations of YG15, ZL108 and 45 carbon steel surface micro-patterns after EDM are made by VHX-600 3D digital microscope. Form the experimental results, we can explain why ZL108 and 45 carbon steel are tractable metals, while YG15 is difficult-to-cut metal.