The invention discloses a forming method for a combined packaging bag and a locating device for the combined packaging bag. The forming method comprises the steps of feeding, accordion edge locating, thermal bonding between an accordion edge and a lower film, point scalding between an upper film and the lower film, thermal bonding between the upper film and the lower film, punching and the like. Because a lower film cursor is used as the locating reference of a second photo-electrical eye and a third photo-electrical eye and thermal bonding between the accordion edge and the lower film is achieved, a position error generated between the upper film and the lower film will not influence the relative positions between the accordion edge and the upper film, the overall structure of the packaging bag will not be damaged, only the position error of the pattern of the upper film is influenced, namely, the pattern of the upper film and the pattern of the lower film will be staggered slightly, and the stagger is within an allowable tolerance range. In this way, the yield of products is high.