The invention discloses a manufacturing method for a slot forming type commutator. The manufacturing method sequentially comprises the following processes of: warm extruding, drawing, punching, segment ranking, compressing, curing, inner hole turning, excircle turning, sanding and polishing, wherein the segment ranking process means ranking commutator segments firstly, and then inserting and ranking inner mica sheets with the same width as that of an insulation slot and outer mica sheets with the width narrower than that of the insulation slot in sequence; and the compressing process means removing the outer mica sheets so as to naturally generate the insulation slot between the commutator segments and make residues not exist in the insulation slot between the commutator segments. In the manufactured slot forming type commutator, the width of an insulation layer between the commutator segments is the same as that of the insulation slot. By the manufacturing method, the conventional slot milling process is omitted, the materials of the commutator segments cannot be wasted, and the insulation performance among the commutator segments is effectively improved so as to improve the yield of commutator products, lower production cost and improve technical performance and quality of the products.