In micro EDM, the behavior of bubble plays an important role in the narrow gap area. It influences the exchange of dielectric, exhaust of debris and so on. Moreover, the behavior of bubble in different hole depth is different since the change of gap width and discharge process. In this paper, the behavior of bubble in different hole depth was observed by a high-speed camera. The number of bubbles was counted from the entrance of micro hole in different depth by a self-made sandwich workpiece in different depth. Moreover, the number of bubble in different current density were counted and analyzed.
