The invention discloses a bag opening device for packing bags. The bag opening device comprises a base, the base is provided with a motor, a cam, a support, a first air inflation bag fixedly connected with the support, a gear and racks meshed with the two ends of the gear, and a rotating shaft of the motor is fixedly connected with the cam; the top and the bottom of the first air inflation bag are each provided with an elastic iron sheet, and guide grooves are formed in the elastic iron sheets; a supporting rod is arranged on one side of the gear, and a protrusion is arranged on the side wall of the supporting rod; a second air inflation bag is arranged on the other side of the gear, and a trigger switch is arranged on the side wall of the second air inflation bag; an air inlet pipe is communicated with the second air inflation bag and the first air inflation bag, and is provided with an air inlet valve; a connecting plate is arranged on the side wall of the rack, and an inclined block is arranged at the bottom of the connecting plate; an L-shaped spraying nozzle is arranged on the connecting plate; a material storage chamber is arranged in the connecting plate; and an air power mechanism is arranged in the material storage chamber. According to the scheme, the problem that the bag opening efficiency of traditional packaging bags is low is mainly solved.