Steel-plastic composite pipe, based on seamless steel pipe and welded steel pipe, with an inner surface coated with high-adhesion, corrosion-resistant, food-grade sanitary polyethylene powder coating or epoxy resin coating. The water supply galvanized inner plastic-coated composite steel pipe, manufactured through pretreatment, preheating, internal coating, leveling, and post-treatment processes, is an upgraded version of traditional galvanized pipes. Steel-plastic composite pipes are generally connected by threaded, grooved, or flanged joints.