The invention discloses a quantitative packing scale. The quantitative packing scale comprises a rack and an operation panel installed on the rack, wherein a platform face is connected with the upper end of the rack, a feeding mechanism is arranged at one end of the platform face, a feeding inlet of the feeding mechanism is connected with a material bin, an inner hopper which is connected with a discharging outlet of the feeding mechanism is arranged at the other end of the platform face, a bag clamping device which is used for hanging packing bags is arranged on an outlet of the inner hopper and on the rack, and a weighing sensor is arranged on the bag clamping device. The quantitative packing scale further comprises a negative-pressure degassing device, wherein the negative-pressure degassing device comprises a vacuum tube which can vertically move, the upper end of the vacuum tube is connected with a vacuum pump, and the lower end of the vacuum tube is connected with a plurality of micro-hole tubes which can be inserted into the packing bags. Due to the fact that the negative-pressure degassing device is additionally arranged, gas in powdery materials in the packing bags can be removed, the size of the powdery materials can be reduced, the bulk density is increased, the powdery materials can be placed into the corresponding packing bags in a filling mode, the quantitative accuracy is ensured, labor intensity of staff is reduced, and efficiency is improved.