Fusion bonded polyethylene (PE), ethylene-acrylic acid copolymer (EAA), epoxy (EP) powder, non-toxic polypropylene (PP), or non-toxic polyvinyl chloride (PVC) are applied to the inner wall of steel pipes to form a steel-plastic composite tube with a thickness of 0.5 to 1.0mm. This material not only retains the high strength, ease of connection, and resistance to water flow冲击 of steel pipes, but also overcomes the disadvantages of steel pipes, such as corrosion, pollution, scaling, and the low strength and poor fire resistance of plastic pipes. The design life can reach 50 years.