Abstract: During the electric discharge machining (EDM) process, the state of the medium in the gap between the poles changes from clear paraffin to paraffin with processing chips and bubbles. The distribution of discharge points is significantly affected by the debris and bubbles, consequently impacts the machining efficiency and quality. In order to reveal the influence of the inter-polar medium state on the distribution of discharge points, an EDM device is constructed by transparent materials, and different concentrations of debris and different volume fractions of air bubbles are placed quantitatively in the inter-polar gap, so as to observe the distribution of discharge points during single-pulse and continuous-pulse discharging processes. The results of the study can provide a theoretical basis for controlling the EDM process conditions and maintaining a good state of the inter-polar medium, so as to improve the efficiency and quality of EDM.