In order to operate in narrow space, a novel miniaturized EDM (Electro Discharge Machining) mechanism has been developed. A prototype of miniaturized EDM device based on ultrasonic motor (UM) has been developed, which has its advantage of compact size (70×40×50 mm). The differential driving electrode has been presented, and coaxial forced vibration of electrode is benefit for the evacuation of debris, so it helps to achieve stable and efficient machining. Driving principle of ultrasonic motor is analyzed, and simulation using Finite Element Method (FEM) is accomplished. The auto-frequency tracking has been carried out, in order that the motor work on resonant or quasi-resonant frequency. Finally, EDM experiment has been finished, and holes with figures of circleΦ85μm and Y-typed have been machined.