The invention provides an automatic polishing system for a cylindrical workpiece. The automatic polishing system comprises a feeding mechanism, a feed mechanism and an outer circle polishing mechanism. The feeding mechanism comprises a feeding rack, a conveying table unit and a pressing unit, and the conveying table unit and the pressing unit are mounted on the feeding rack. The feed mechanism is mounted on a support face plate of the feeding mechanism and comprises a feed rack and a motion control unit mounted on the feed rack. The outer circle polishing mechanism comprises a polishing rack, a motion unit and a polishing unit, and the motion unit and the polishing unit are mounted on the polishing rack. The polishing unit comprises linear guide rails, a sliding base, a stepping motor support, a driving wheel, a lead screw, a servo motor, a sanding belt, a tensioning wheel, a driven wheel and a stepping motor. The automatic polishing system can completely replace manual operation, work efficiency is remarkably improved, manpower cost is reduced, and the automation level of an enterprise is improved; and all polishing parameters are precisely controlled, and the more stable and better polishing quality can be achieved.