Clamp for finely milling top surface and finely boring cylinder hole on thin-walled cylinder block

The invention discloses a clamp for finely milling a top surface and finely boring a cylinder hole on a thin-walled cylinder block. The clamp comprises a base, a left supporting arm, a right supporting arm, a pressing plate assembly and a holding rod assembly, wherein the base is L-shaped; a thrust gear locating pin boss and a rear end locating pin boss are relatively arranged in the middle of a vertical plane of the base; a thrust gear locating pin and a rear end locating pin are arranged on the vertical plane of the base; the pressing plate assembly comprises a supporting seat, a spring, a pressing plate, a clamping screw, a screw bushing and a supporting block; the clamping screw is in a stepped shaft structure; pressing plate steps are arranged in the middle of the clamping screw; the supporting seat is fixed at the outer side of the thrust gear locating pin boss; the pressing plate is pulled on the supporting seat through the spring; the supporting block is fixed at the right side of the thrust gear loca