Abstract: The method of improving the surface roughness of Al powders by acid etching Al powders was used to obviously reduce the glossiness of Al-popyurethane(PU) composite coatings under the premise of not obviously raising the infrared emissivity of the coatings. The effects of acid etching time of Al powders on the microstructure, glossiness, infrared emissivity and mechanical properties of the Al-PU composite coatings were systematically studied. The results show that acid etching of Al powders can significantly reduce the glossiness of the coatings. Acid etching 10 min can make the coating's glossiness decrease from 20.1 to 13.0, but it has no obviously effect on microstructure of the coatings. And the effect on the emissivity of the coatings is very limited. Acid etching 50 min only can make the coating's emissivity increase from 0.208 to 0.254, still has a lower emissivity. Acid etching 20 min can make the coatings have lower glossiness and emissivity which are 12.8 and 0.228, respectively. The mechanical properties of the coatings are not sensitive to acid etching of Al powders, the hardness, adhesion strength and impact strength of the coatings before and after the treatment can reach 3 H, 1 grade, and 50 kg·cm, respectively.