The utility model discloses a fixed-length splitting device of a plastic bag. The fixed-length splitting device comprises a workbench, wherein a barrier strip is arranged at certain position of the workbench, the distance between the edge of one end of the workbench and the barrier strip is just equal to the length of the plastic bag; two sides of the workbench are respectively and fixedly provided with a supporting rod, a strut is fixed between the upper ends of the supporting rods on the two sides of the workbench, the supporting rods on the two sides of the workbench are further and respectively hinged with a movable rod, a connecting rod is fixedly arranged between the two movable rods, and a spring is connected between the strut and the connecting rod; and a blade is fixedly arranged between the front ends of the two movable rods, and the edge of the blade is used for cutting when the edge is dead against the workbench and the blade is just propped against the edge of the barrier strip. The fixed-length splitting device disclosed by the utility model has a smart structure design; a preset position of the barrier strip keeps the cutting length of the plastic bag, and the cutting length of the plastic bag does not need to be measured for each cutting; and in addition, the cutting operation is convenient and quick, and the operation efficiency is high.