Abstract: The absence of film defect monitor in CV carton overwrapper in GD packing line resulted in film-associated defects,such as film missing and distortion,remaining in finished cartons.Therefore,a carton film monitor was designed,which was composed of reflective optical fiber sensor,opposite optical fiber sensor,carton synchronous sensor,carton position sensor and PLC.The cartons with film defects would be rejected at the entry of the S-shape lifter without stopping the packing machine.After improvement,the defect rate of finished products reduces from 20 to 25 carton/day to 0.1 to 0.2 carton/day.The monitor is easy to be installed and adjusted,and it is reliable.