The work aims to study the effect of Al2O3 on the properties of Cr2O3/TiO2/Al2O3/SiO2 quaternary composite ceramic coating. The composite ceramic coatings with different Al2O3 contents were deposited on the surface of X80 pipeline steel by plasma spraying. In addition, all coatings were prepared on preheated and unpreheated substrates to show the effect of substrate temperature on the coating properties. Then, the porosity, hardness, adhesion and electrochemical corrosion performance of the coatings were measured by boiling weighing method, Vickers hardness tester, scratch tester and electrochemical workstation, respectively. The phase composition and morphology characteristics of the coatings with different Al2O3 contents were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of substrate temperature and Al2O3 content on the coating properties were studied. With the increase of Al2O3 content, the porosity of Cr2O3/TiO2/Al2O3/SiO2 quaternary composite ceramic coating decreased firstly and then increased, while the adhesion and dimensional hardness of the corresponding quaternary composite ceramic coating increased firstly and then decreased. When Al2O3 mass fraction was 60%, the performance of the quaternary composite ceramic coating was the best, with porosity of 3.6%, hardness of 824.6HV and adhesion of 53.8 N. The electrochemical corrosion test showed that the corrosion resistance of the coating was improved by Al2O3. When Al2O3 mass fraction was 60%, the self corrosion potential of the coating was the highest, -0.28 V. In addition, under the preheating and unpreheating conditions, the properties of the coating varied with the Al2O3 content, but preheating was more beneficial to improving the coating properties than unpreheating. The addition of Al2O3 can not only effectively reduce the Cr content of the coating, but also significantly improve the properties of the quaternary composite ceramic coating, especially the corrosion resistance. In addition, the substrate should be preheated before plasma spraying, which is beneficial to improving the coating properties.