Abstract: Alumina-based ceramic coatings with different content of boron nitride (BN) were prepared on Q235 substrate using a thermochemical reaction method and composite phosphate as the adhesive. The effects of BN content on the morphology and microstructure, thermal expansion coefficient, and high-temperature chloride corrosion resistance of thermochemical reactive ceramic coatings were studied using scanning electron microscopy and X-ray diffraction. The results indicate that a new phase of Al_0.67Fe_0.33Po₄was formed by the reaction between the thermochemical reaction coating and the substrate. As the BN content in ceramic coatings increased, the cracks and pores on the coating surface first decreased and then increased. The thermal expansion coefficients of 30% BN-Al₂O₃and 50% BN-Al₂O₃ceramic coatings were 7.9×10^-6 and 7.7×10^-6 respectively, which were relatively close to the matrix material Q235. Ceramic coatings significantly improved the high temperature chlorine corrosion resistance of Q235 steel, and 50% BN-Al₂O₃ceramic coating had the best high temperature chlorine corrosion resistance.