The invention relates to a size-adjustable carton hemming device. The pressing device includes a pressing plate, which is connected with a positioning plate, and a positioning hole is arranged on the pressing plate, and a pressing long plate and a pressing plate are fixed in the positioning hole. Pressing down the short plate, the pressing down long plate and the pressing down short plate both include a pressing down fixing plate, the two ends of the pressing down fixing plate are connected to the extension block through the extension plate, the pressing device includes a supporting plate, and the outer periphery of the supporting plate is sequentially provided with a second A pallet frame and a second pallet frame, the second pallet frame is provided with an adjustment plate on the outer periphery, and a push plate is provided on the adjustment plate, and the adjustment plate includes an adjustment plate fixing block, and the two ends of the adjustment plate fixing block are connected and adjusted by an extension plate The plate extension plate, the push plate includes a push plate fixing block, the two ends of the push plate fixing block are connected to the push plate extension plate through the extension plate, the positioning plate, the pressing plate, the adjustment plate, the push plate, the supporting plate, the first supporting plate Both the frame and the second pallet frame are connected to the cylinder through the piston rod, which is a size-adjustable carton hemming device that can meet the hemming of cartons of various sizes.