Machining device and method for large-diameter small semicircular hole

The invention discloses a machining device and method for a large-diameter small semicircular hole. The machining device comprises a cutter head base, a first rough boring cutter, a second rough boring cutter, a fine adjustment cutter, a first measuring assembly, a second measuring assembly and a dial indicator, wherein the cutter head base is fastened on a machine tool power accessory and is provided with a plurality of cutter grooves; the first rough boring cutter is used for rough boring and is fixed in the cutter groove of the cutter head base, and the second rough boring cutter is the same as the first rough boring cutter in structure, is used for secondary rough boring cutting and is fixed in the cutter groove which is adjacent to the first rough boring cutter and is located behind the first rough boring cutter; the first measuring assembly is used for measuring rough boring and is mounted in the area of the second rough boring cutter; the fine adjusting cutter is used for semi-fine boring and is mounte