The invention provides a string sheathing forming device, which belongs to the technical field of machinery, and solves the problem of poor stability in the prior art. The forming device comprises a frame and a molding cylinder, wherein the molding cylinder has a long cylindrical shape, and cylindrical molding cavities are arranged in the molding cylinder along longitudinal direction. The formingdevice further comprises a screw and a driving component, wherein the screw is axially fixed in the molding cavity, and the driving component is fixedly attached to the frame. The driving member is connected to the screw, the number of the molding cavities is two, and the two molding cavities are arranged in parallel and the two sides are connected to each other. The screw and the driving member form a molding unit, and each of the molding cavities has a corresponding molding unit. The forming device has high stability.