Abstract: The composition protective coatings on the surface of carbon steel crucible were prepared by aluminizing and high temperature chemical reaction. The relations between the thickness of reaction product layer and reaction temperature and time were investigated. The microstructures and phase composition of the coating layer were investigated by means of optics microscope and XRD. The experimental results show that the thicknesses of reaction product layers increase with the reaction temperature and time increasing. The composition coatings are composed of transition layer and reaction product layer. The constitution of transition layer are Fe₃Al and small amount of Fe₂Al₅, Fe₁₄Al₈₆ and Al₂O₃. The reaction product layer are consisted of TiB₂, MgO and small amount of Mg₂TiO₄, Mg₂B₂O₅, Fe₃Al, FeAl and Ti₂B₅.