The invention discloses a novel carton opening mechanism simultaneously suitable for corrugated cartons of different specifications. The carton opening mechanism comprises a rack, vertical guide rails, a vertical lead screw, a suction disc set, a baffle, a moving push rod, a synchronous belt linear moving unit, a linear air cylinder and a magnetic rodless air cylinder. The carton opening mechanism conducts carton opening work through joint matching of vertical moving and horizontal moving of the suction disc set and with the assistance of the baffle and can complete the carton opening work of the corrugated cartons of the different specifications on the same machine. The baffle is vertically fixed to the rack, the side face of the baffle is aligned with middle folds of all the corrugated cartons (in the folded state) of the different specifications on a corrugated carton shelf, in the process that the suction disc set pulls the corrugated cartons of the different specifications, one small side faces of carton bodies are blocked, and thus the carton opening work can be completed. Through the magnetic rodless air cylinder, the length of the rack in the horizontal moving direction of the suction disc set is reduced while the effective working space is guaranteed.