A device for insulating a cathode surface in electrochemical machining is provided. The cathode surface insulation device is characterized in that super-hydrophobic micro-structures are prepared in regions to be insulated on the cathode surface, so as to realize selective insulation of the surface of the tool cathode, and thereby achieve objects of constraining an electrical field in the processing area, reducing stray corrosion and side surface taper, and improving processing efficiency and accuracy.