Abstract: For positively positioning carton blank in YB65A cartoner to eliminate folding failures caused by paperboard defects, a device for positioning the long sides was designed, it was arranged between long side folders and fixed guide plates. Driven by a cylinder, the positioning plates in the device moved forward and downward along guide rails to hold the folded long sides in folded shape. The results of application showed that:the device was simple in structure, and convenient in installing and dismantling, the blanks were in positively positioning and the folding of carton blank was effectively ensured. The machine failures caused by passage jam or damage decreased from 2-5 times to 0 per month, the resetting of machine for adapting to carton blanks of different characteristics was avoided, and the machine efficiency increased by 1 percentage point.