When the quantitative packing machine for mixtures manually sets the bags into the lower outlet, it moves the clamp switch. The control system receives the signal of the bags and drives the cylinder. The clamp clamps the bags. At the same time, it starts the feeding mechanism to feed the materials into the packing scale. The feeding mechanism is the belt feeding mechanism. The fast feeding (big head feeding) is used to feed the materials. When the target weight of the fast feeding is reached, the fast feeding can be done quickly. Material stops closing the feeding door, controlled by the instrument, slow feeding (small end feeding) for slow feeding. When the required target weight is reached, slow feeding stops, the belt opener opens automatically, the packaging bag falls on the conveyor automatically, and the conveyor delivers the packaging bag back to the seam outlet to complete a bag filling process.