The utility model relates to a split type forming cutter machining a stepped hole transition conical surface. A trapezoid groove matched with a stepped hole is formed in the middle of a cutter clamp. Blades are arranged in cutter grooves in the two sides of the cutter clamp. Adjusting screws adjusting the positions of the blades are arranged at the bottom of the trapezoid groove. Pressing screws fastening the blades are arranged on the cutter groove sides. The installing directions of the blades on the two sides are opposite, and cutting edges face upwards and downwards respectively. The split type forming cutter is inserted into a boring head cutter hole matched with the split type forming cutter in taper and bores into the large hole conical surface starting point from the large hole port, and the large and small hole transition conical surface machining is finished through longitudinal feeding. The cutter clamp and the blades are split, and the blades can be adjusted and replaced and can be used through multiple times of repeated cutter grinding. The taper degree of the blades is adjusted by adjusting the adjusting screws at the large end and the small end of the cutter clamp, and it is guaranteed that the taper of the blades is consistent with the taper of the inner hole transition conical surface degree of workpiece drawing. The pressing screws fasten the blades. The trapezoid groove of the cutter clamp is adopted, the weight is reduced, and installing of the adjusting screws is facilitated. The cutter clamp can be repeatedly used, and the blades can be adjusted or replaced after being damaged.