In this paper, the system uses cold extrusion to process the big diameter internal thread of high strength steel on the basis of the fundamental of metal plastic forming. The workpiece’s organization structure is improved because of plastic formation of organizational structure. Favorable surface integrity of workpiece is obtained, and mechanical properties are improved. This paper aims at higher extrusion torsion, low thread accuracy, rejecting rate high, vibration tapping is adopted to obtain high quality in the processing interior thread with big diameter.