A Ti0.7Al0.3N coating was deposited on 1Cr11Ni2W2MoV stainless steel by arc ion plating. The oxidation behavior in air and corrosion resistance under NaCI deposit in wet air at 450 ℃ of the coating were investigated. The results show that the Tio.T0.7Al0.3N coatings exhibited excellent oxidation resistance in air at 450℃, severe corrosion happened to the stainless steel, while a great enhancement in corrosion resistance occurred to the substrate with Ti0.7Al0.3N coatings. The porous oxides with inner layer rich in Cr and outer layer rich in Fe formed on the 1Cr11Ni2W2MoV stainless steel, while dense oxides mixture of Al2O3 and TiO2 appeared to the coatings after corrosion which greatly inhibited the inwards diffusion of O and HCI and enhanced the corrosion resistance. The mechanism of the effect of water vapor and NaCI on corrosion of Ti0.7Al0.3N coatings was proposed.