Abstract: An automatic carton slitting machines includes a transmission means for moving cartons, a sensing and positioning means for detecting and positioning the cartons at locations desired, a slitting means for slitting the carton and a control unit for coordinate and control the operations of all other means. The cutter means includes two spaced cutter sets each has a motor driven rotating saw cutter with adjustable slitting angle. One of the cutter sets is movable by a cutter set moving means for changing spacing distance between the cutter sets to process carton of different width. The cutter means also has a frame lifting means to adjust cutter sets height for processing cartons of different height. Through coordinating the transmission means, cutter set moving means and frame lifting means may coordinate their motion so that the cutter sets may move in three dimensions against the carton for automatically cleaving cartons of different size.