As the electro-erosion theory, the hydrocarbon is decomposed into large quantity of carbon under high temperature that the discharge ionization creates. The carbon is coated on anode under the electric field. This phenomenon is used as the electrode compensation in the process of EDM shaping. But during wire cutting, some carbon is carried out of the joint-cutting, some is covered on the surface of workpiece. It has the character there is less carbon near the wire entrance and more near the wire exit. That is why the black-and-white dog-teeth staggered stripe occurs. The adhesion of coating is changing as the temperature between the workpiece and the discharge channel, also as the electric-field intensity. The carbon coating occurs companied with the electro-erosion process. As long as processing, the stripe will occurs. The carbon coating usually is 0.01-2μ. It’s difficult to clean it. Only clean it thoroughly by polishing and removing the pit. It’s not big problem if only there is the carbon coating without the shaped fit. How to make the stripe become light: reduce the consistency of the coolant; decrease the process voltage; trace frequency conversion more close.