The invention belongs to the technical field of petroleum equipment machining and manufacturing, and particularly relates to a combined tool and method for machining a petroleum drill pipe tool jointwith a stress groove. The combined tool comprises a beveled turning tool body, a thread tool body and a stress groove turning tool body; the beveled turning tool body is a rhombic tool and is used forturning a threaded conical surface, a plane part of the stress groove and a plane part of a pipe end of the petroleum drill pipe tool joint with the stress groove; the thread tool body is a carding tool or a single-tooth tool and is used for turning the threaded part of the petroleum drill pipe tool joint with the stress groove; the stress groove turning tool body is a rhombic tool or a forming grooving cutter and used for turning the stress groove part of the petroleum drill pipe tool joint with the stress groove. Due to the turning with the three tool bodies, the usage amount and the replacement frequency of the tool bodies are greatly reduced while the thread machining precision is ensured, the machining efficiency is improved, and the production cost is reduced.