A hole shrinkage prevention reamer comprises a reamer rod. At least two tool bits are evenly arranged on the circumferential face of the front end of the reamer rod. The rear end of the reamer rod is provided with a flange connecting structure. A groove which is large in the outer portion and small in the inner portion and of a conical structure is formed in the center of the front end face of the reamer rod in the axial direction. A threaded hole is formed in the portion, at the center of the bottom of the groove, of the reamer rod in the axial direction. An adjustment bolt is connected in the threaded hole through threads. The head portion of the adjustment bolt is of a conical structure with a large outer portion and a small inner portion. The head portion of the adjustment bolt adapts to the inner wall of the groove and is matched with the inner wall of the groove in an ejecting and pressing mode. The hole shrinkage prevention reamer is novel in design, simple in structure, easy to machine and manufacture and convenient and rapid to assemble and disassemble, the fine tuning structure is additionally arranged at the center of the edge of a tool, the service life of the tool can be prolonged, and the hole shrinkage phenomenon can be avoided.