Aiming at the problem that it is difficult to detect the discharge state of narrow pulse width and small duty cycle pulse, this paper studies the variation characteristics of inter electrode impedance in micro-EDM process, puts forward a detection method to distinguish different discharge states in micro-EDM based on the change of electrical signal caused by the change characteristics. The influence of pulse width and duty cycle on the quality of micro-EDM is analyzed. The surface machining quality of workpiece can be improved obviously by compressing the pulse width of pulse power supply. And designs a discharge state detection system based on inter electrode impedance variation characteristics. Experiments verify the detection method, and test the machining effect of the control strategy through the trial machining experiment, which ensures that the micro-EDM process is efficient and stable.