The invention discloses an automatic ribbon cutting device for ribbon attaching of packaging boxes. The device is characterized in that a ribbon cutting air cylinder is mounted on a ribbon cutting mounting frame, wherein the upper end of a tool mounting seat is fixedly connected with the lower end of a piston rod of the ribbon cutting air cylinder, the upper end of a ribbon cutting tool is mountedat the lower end of the tool mounting seat, and a ribbon cutting supporting block is located right below a cutter of the ribbon cutting tool; a ribbon pressing air cylinder is mounted on a ribbon pressing mounting frame, wherein a ribbon pressing block is fixedly connected with the lower end of a piston rod of the ribbon pressing air cylinder, and a ribbon guide block is mounted at the position between the portion between a ribbon pressing supporting part and the ribbon cutting supporting block; and the ribbon guide block is provided with a guide groove or a guide through hole for ribbon to pass through, and the ribbon cutting air cylinder and the ribbon pressing air cylinder are condescendingly connected with a controller. According to the automatic ribbon cutting device for ribbon attaching of the packaging boxes, the high-precision, high-quality, high-efficiency and automatic operation of the ribbon cutting process is realized, and the overall automation process of packaging box production is promoted.