The double-sided color steel polyphenyl composite air duct uses 25 mm thick polyphenyl insulation material as the interlayer, and the inside and outside are compounded with color steel plates of different thicknesses (0.3~0.5 mm). Flanges of different materials (bridge cutoff aluminum alloy, semi aluminum alloy, PVC) can be selected. The finished air duct produced by automatic machinery does not need secondary insulation, and is hoisted in modular combination.