Fusion-bonded polyethylene (PE), ethylene-acrylic acid copolymer (EAA), epoxy (EP) powder, non-toxic polypropylene (PP), or non-toxic polyvinyl chloride (PVC) are melted onto the inner wall of steel pipes to form a steel-plastic composite pipe with a thickness of 0.5 to 1.0mm. This material combines the high strength, ease of connection, and resistance to water flow impact of steel pipes, while overcoming the drawbacks of steel pipes, such as corrosion, contamination, scaling, and the low strength and poor fire performance of plastic pipes. The design life can reach 50 years.