The four-station pre-made bag packaging machine features four stations: bag removal, bag opening, filling, and sealing. These stations work together continuously to automatically remove, open, quantitatively fill, and seal the pre-made bags, eliminating the need for manual intervention. The machine can package stand-up pouches, four-side seal bags, eight-side seal bags, zipper bags, and special-shaped bags, though mold adjustments are required depending on the machine model (e.g., M-bags and vacuum bags require special configurations).