The invention discloses an die opening and closing mechanism, which belongs to a plastic product molding machinery and comprises a pair of die-set guide rail bases, a left die set, a right die set and a pair of synchronous running gears, wherein the upper surface of one end of the die-set guide rail base is fixedly provided with a left die-set linear guide rail, the upper surface of the other end is fixedly provided with a right die-set linear guide rail; the left die set is assembled on the left die-set linear guide rail; the right die set is assembled on the right die-set linear guide rail; the synchronous running gear comprises a power machine, a power machine base, a driving wheel, and a first and second draw bars; the power machine base is arranged outside the middle part of the length direction of the die-set guide rail base; the power machine is arranged on the power machine base; the driving wheel is fixed on the power machine and positioned in the driving wheel cavity of the power machine base; one end of the first draw rod extends into the driving wheel cavity to be matched with the driving wheel, and the other end is connected with the lower part of the right die set; and one end of the second draw rod extends into the driving wheel cavity to be matched with the driving wheel, and the other end is connected with the lower part of the left die set. The invention omits a die opening and closing oil cylinder and ensures the precision of opening and closing the die, and saves the energy.