The invention relates to a self-adaptive bag clamping device which has the following structure that two long flange bearings and a long bag opening air cylinder are respectively arranged on the same beam and are fixed; two long guide rods are connected with a guide rod beam after respectively penetrating through the two long flange bearings, a piston rod of the long bag opening air cylinder is connected with the guide rod beam through a floating connector, and the guide rod beam is fixed together with a bag opening plate; the fixed end of a bag clamping part and a bottom plate are fixedly arranged on a mounting seat, and the regulating end of the bag clamping part is inserted to a slot formed in the bottom plate of the bag clamping part; a bag pressing strip is arranged below the bag clamping part and is fixedly arranged on a bag pressing guide rod connecting plate; a bag pressing air cylinder and two bag pressing guide rod flange bearings are respectively arranged on a bag pressing air cylinder frame, two bag pressing guide rods are connected with the bag pressing guide rod connecting plate after respectively penetrating through the two bag pressing guide rod flange bearings, and a piston rod of the bag pressing air cylinder is connected with the bag pressing guide rod connecting plate; and the beam is arranged on the mounting seat through two upright posts. The self-adaptive bag clamping device has the characteristics of simple and compact structure and wide application range and is capable of keeping regular, ordered and beautiful filling effects, stable in working state and relatively low in cost.