The utility model discloses an edge folding device for plastic bags. The device comprises a machine frame, two ends of the machine frame are respectively provided with rollers, the plastic bags in rolls are sleeved on the outside of a roller on one side, a plurality of parallel traction shafts are installed between the rollers on the machine frame in rotating mode, a support plate is fixed below one traction shaft on the machine frame, the left end face and the right end face of the support plate are respectively recessed to form concave cavities, the left side and the right side of the support plate are respectively provided with clamp plates, the clamp plates extend into the left concave cavity and the right concave cavity of the support plate, the plastic bags in rolls wind on the traction shafts to be sleeved on the outside of the support plate, the clamp plates on the left side and the right side of the support plate butt against the outsides of the plastic bags to form folding edges, and the plastic bags are continuously drawn to wind on the traction shafts to be rolled to the outside of the roller at the other end. The edge folding device for plastic bags is ingenious in structure and automatically draws the folding edge in the whole process, and the whole device is compact, good in performance and convenient and fast to operate and improves working efficiency.