The physical model of the ultrasonic vibration assisted electric discharge machine (EDM) compound machining of work was established, and by using finite element software ANSYS, the temperature field simulation analysis was carried out on the 45 steel. The rules of influence on pit appearance were analyzed and obtained by the power density, peak current and pulse width. Through the test collected data, by the verification of Matlab software to render the image analysis, it is found that the theory results are basically in consistent.