Wire EDM is the continuous movement of the fine metal wire (known wire electrode) electrode and the workpiece of pulse EDM except for metal, cutting and forming a processing machine. Loose contact wire between the electrode and the workpiece processing online existing light pressure discharge phenomenon. When the flexible wire electrode and the work piece close to usually think of discharge gap (e.g. 8 ~ 10 m), do not occur spark discharge, even when the wire electrode has come into contact with the workpiece, from the microscope have not see the gap, often fail to see the spark, and only when the workpiece will electrode silk top bending and offset a certain distance (a few microns to tens of microns) to normal spark discharge. This wire electrode feed per 1 m, discharge gap does not reduce 1 m, but wire electrode increased tension between a bit line, the workpiece is increased a little lateral pressure, obviously, only wire electrode and a workpiece between keep some minor contact pressure to form a spark discharge. It is believed that there exist some kind of insulating film medium between the electrode wire and the workpiece.