The invention discloses a bag opening and positioning tool of a packaging machine. The tool comprises a fixed seat, a lifting mechanism fixed to the fixed seat and a bag opening clamp which is connected to the top end of the lifting mechanism and is in bilateral symmetry; the lifting mechanism comprises a lifting driving air cylinder and a lifting rod, wherein the lifting driving air cylinder is fixed to the bottom end of the fixed seat, and the lifting rod is connected with the lifting driving air cylinder; the bag opening clamp comprises a U-shaped mounting frame fixed to the top end of the lifting rod, a movable guide rail fixed to the top end of the U-shaped mounting frame, two clamping plates which are mounted on the movable guide rail in a sliding manner and provided with opposite inner end faces and a clamping plate driving air cylinder connected with the clamping plates; and the lifting driving mechanism and the clamping plate driving air cylinder are both connected with a master controller.