The invention discloses a forming method of an overhead line system supporting device. The forming method of the overhead line system supporting device comprises the following steps that (1) a core tube is processed into a horizontal cantilever (1), an oblique cantilever (2), an arc arm (3) and a connecting arm (4), and the horizontal cantilever (1), the oblique cantilever (2), the arc arm (3) and the connecting arm (4) are bonded; (2) the core tube is wound with prepreg; and (3) mold assembly and curing formation are performed. By means of the forming method of the overhead line system supporting device, the overhead line system supporting device is prepared simply and efficiently; and meanwhile, the prepared overhead line system supporting device is low in weight, high in strength and suitable for various climate conditions and has excellent insulating performance, the reliability of an overhead line system can be improved, and the installation and maintenance work difficulty can be reduced.