The invention relates to an open-close type zero sequence current mutual inductor cutting method, including the following steps: 1, a hard alloy disc blade which has the thickness of 2-10mm, tooth number of 60-200 and outer diameter of 120-300mm and is used for cutting aluminium is arranged on a common horizontal milling machine; 2, a mutual inductor to be cut is tightly compressed on a worktableby a bolt and a pressing plate; 3, the spindle speed of the milling machine is adjusted to be 30-150r/min, advancement of the worktable is adjusted to be 23.5-60mm/min, a cutter is manually aligned to the cut position specified by the mutual inductor, the milling machine is started, a cooling system is open, the exit of cooling liquid is aligned to the cut position, self-acting feed is adopted, cutting is carried out on one side of the mutual inductor until the other side of the mutual inductor is cut through; 4, the other side of the mutual inductor is manually moved to the disc blade position, self-acting feed is adopted, and cutting is carried out on the other side of the mutual inductor. The existing universal machine tool is utilized to cut through the entire zero sequence current mutual inductor, processing efficiency is greatly improved, and processing cost is greatly reduced.