To the appropriate solution, chemical or chemical methods with microscopic rough surface parts for processing, can obtain mirror polishing and leveling finishing processing surface. Electrolytic polishing is often used to finish the surface of some tools, or to make highly reflective surfaces and metallographic test pieces. Electrolytic polishing is the etching of metal parts as anodes under specific conditions. In the process of electrolysis, thick mucous membrane with high resistivity was formed on the anode surface. The thickness of this layer of mucosa is less in the microscopic convex part of the surface, and larger in the microconcave part. Therefore, the microscopic distribution of current density is not uniform. The microcosmic bulge has a higher current density and the solution is faster, while the microcosmic concave has a lower current density and the solution is slower. In this way, the size of the microcosmic bulge is reduced and slowed down, so as to achieve the purpose of leveling and shining. This is the mucosal theory. The oxide film theory holds that all the convex parts form oxide films, but the oxide film in the convex part is loose, the anode current density is high, and the oxygen production is more, so that the oxide film in the convex part is formed and dissolved faster than that in the concave part, and repeated to make the plane smooth.