The invention provides a reducing rotary cold extrusion strengthening process device. The reducing rotary cold extrusion strengthening process device comprises a mandrel, as well as a lining and a fixed drum that are arranged on the mandrel in a sliding and sleeving manner and are fixedly connected with each other, wherein the lining consists of a plurality of fan-shaped lining blocks in circumferential arrangement; the other end of the fixed drum, away from the lining, is connected to a motor and a pipeline system; the mandrel comprises a conical cylinder and a constant-diameter cylinder; a conical through hole is formed in the lining; each fan-shaped lining block comprises a body and a lug boss; and spherical bulges in close and regular arrangement are formed on the outer surface of thebody. Owing to the spherical bulges in close arrangement on the surface of the lining, the fatigue life of a processed inner hole is favorably prolonged. The mandrel is designed into a conical cylinder, so that an adverse effect on the extrusion accuracy from abrasion of a square mandrel is avoided. Moreover, hole extrusion and the reaming process are combined to improve the degree of finish of the surface of the processed inner hole, so that the processing continuity is guaranteed, and the processing accuracy and the processing efficiency are improved.