The three in one structure of polyurethane prefabricated buried insulation pipe is formed by tightly bonding the working steel pipe (or steel pipe fittings) and the outer protective pipe through the insulation layer, forming an integrated buried insulation pipe (or insulation pipe fittings) structure. Polyurethane insulation pipe working steel pipes include seamless steel pipes, straight seam steel pipes, and spiral seam steel pipes, made of Q235 series, 20 steel series, and Q345 series materials.