The invention discloses a bag clamping device. The bag clamping device comprises a bag clamping tube, a clamp and two bag clamping air cylinders, wherein the clamp is connected to the lower end of the bag clamping tube in a sleeving manner; the two bag clamping air cylinders are respectively mounted on two sides of the clamp; a bag clamping plate is arranged on a piston rod of each bag clamping air cylinder; each piston rod of the corresponding bag clamping air cylinder stretches out and draws back, so that the bag clamping plates are respectively pressed on or loosened from the outer wall of the two sides of the clamp; the clamp comprises clamp closing air cylinders and two clamp sheets which are oppositely arranged; the upper end of each clamp sheet is hinged to the bag clamping tube; the clamp closing air cylinders are respectively mounted on two sides of the bag clamping tube; a piston rod of each clamp closing air cylinder is connected with the corresponding clamp sheet; and each clamp sheet is controlled by the corresponding clamp closing air cylinder to rotate by using the corresponding hinged point as center to open and close. Bag opening and automatic bag clamping can be completed, and the shape normalization of openings of packaging bags is realized, so that seaming is convenient, and the operation reliability and the feeding efficiency of a full-automatic big-bag packing machine are improved. The bag clamping device disclosed by the invention is reasonable in structure, reliable in performance, and simple and convenient to operate.