The utility model discloses a large-length-diameter-ratio inner taper hole ring groove machining turning tool, and relates to the field of corrugated horn antenna machining. The cutter comprises a cutter head and a cutter sleeve, wherein the cutter sleeve is of a cylindrical cone structure; a columnar step through hole is formed in the cutter sleeve in the axial direction; the tool bit is of a cylindrical cone structure; the cylindrical end of the tool bit extends into the stepped through hole from the conical head of the tool sleeve in the axial direction and is fixedly mounted at the axis ofthe inner wall of the tool sleeve; the axial limiting and fixing of the tool bit are realized at the step of the step through hole of the tool sleeve; the tool bit comprises a tool bit cylinder section, a tool bit cone section, a duck tongue and a connecting rod; the cylindrical section of the tool bit horizontally extends into the tool sleeve; the large-diameter end of the tool bit cone sectionis integrally connected with the tool bit cylinder section; the connecting rod is fixedly connected with the small-diameter end of the tool bit cone section in the axial direction. The duck tongue isvertically and fixedly mounted on the side wall of the axial end surface of the connecting rod; according to the utility model, the corrugated horn antenna which mainly comprises the ring groove and has the advantages of deep characteristics, thin diaphragm and large length-diameter ratio is processed, and the processing precision is high.