The utility model relates to a carton shaping or equipment for packing technical field specifically disclose a paper cassette positioning mechanism, including a platen to and including setting up a backstop and two movable rods on the platen, its characterized in that: the fixed middle part of locating the platen of backstop, the front end of backstop is equipped with the domatic of slope, two movable rods locate the both sides of backstop respectively, and two movable rods all are equipped with and push away the arm, rear end and two movable rods of backstop and push away the location regionthat forms the carton between the arm, two movable rods all connect to be equipped with and be used for driving the drive arrangement that sharp back and forth movement was made to the movable rod, make the arm that pushes away of two movable rods press from both sides two jiaos of rear ends of leaning on to the backstop of carton and accomplish the location, can firmly fix the carton at specificposition, make the fixed back of carton be in quiescent condition, the deviation can not appear or fix a position unsafe phenomenon.