The corrosion behavior of Super304H, HR3C and related aluminized coatings under K2SO4 + Na2SO4 (mass ratio =1: 1) and K2SO4 + Na2SO4 + KCl (45: 45: 10) deposits in a mixed gas of 0.5SO2–4O2–20H2O-75.5CO2 (vol.%) at 700 °C were studied. Super304H undergoes severe corrosion under both deposits, the addition of KCl did not significantly accelerate the corrosion process but resulted in an extremely porous and thickness-doubled scale. While HR3C with higher Cr content shows excellent corrosion resistance in Cl free environment due to the formation of dense Cr2O3. Due to the involvement of Cl, HR3C can no longer resist the corrosion of the salts. The corrosion depth increases by two orders of magnitude and becomes as severe as Super304H. Aluminizing significantly improved the corrosion resistance of the alloys on account of α-Al2O3 formation by a new mechanism. The addition of KCl had little effect on this mechanism and only increased the thickness of the corrosion products slightly.