The invention discloses a method for die-forging a forging piece by adopting a single-arm hoisting ring for petroleum drilling. The method comprises the following steps of: drawing a rod part of a single-arm hoisting ring, firstly, carrying out rough rolling on the rod part, and controlling rod diameter size and length size; rolling the big end and the small end of the single-arm hoisting ring byusing a die; then flattening the big end and the small end of the single-arm hoisting ring, and punching a profiled hole; die-forging the big end and the small end of the single-arm hoisting ring; carrying out flash cutting on the big end and the small end of the single-arm hoisting ring and carrying out hammer flash cutting on a free forging hammer; punching inner hole connected scale for the big end and the small end of the single-arm hoisting ring out; rolling the rod part for the single-arm hoisting ring so that the diameter size of the final rod part and the final length size of the single-arm hoisting ring are obtained, and controlling a pairing length size; and leveling the big end and the small end of the single-arm hoisting ring, and straightening the rod part. According to the method disclosed by the invention, the yield of the single-arm hoisting arm is remarkably improved, and the requirement of a trimming process of the single-arm hoisting ring is completely met.