The invention discloses an electrolytic machining device for a plane zigzag group groove and an electrolytic machining method. The electrolytic machining device comprises a first cavity, a substrate embedded in the first cavity, a workpiece installed on the substrate, a mask plate arranged on the upper surface of the workpiece and provided with a snakelike runner, and a second cavity arranged on the upper surface of the mask plate; wherein a cathode block is arranged on the bottom surface of the second cavity, and an auxiliary liquid supply hole penetrates through a body of the cathode block. As the mask plate is fixed by compressing the surface layer by layer, the tiny liquid flowing runner is formed for electrolytic machining, meanwhile, the auxiliary liquid supply hole is additionally formed in the body of the cathode block to improve the problem of an uneven flow field at the corner of the snakelike runner, in addition, the auxiliary liquid supply hole provides a fresh electrolyte, so that the conductivity of the electrolyte in the whole machining area is kept at a relatively stable level, then plane zigzag microgrooves good in size consistency and higher in surface quality are efficiently machined in the surface of the metal workpiece, and the mask plate is repeatedly used.