Plasma sprayed zirconia (ZrO₂) coating is widely used as thermal barrier coating (TBC) for its good performance in thermal and corrosion resistances. As one problem as TBC, the spallation of the coating is mostly caused by the oxidation at the interface between the coating and substrate. In this study, Al₂O₃+ZrO₂ composite coating as TBC, has been deposited by gas tunnel type plasma spraying, whose mechanical properties are quantified by hardness tester, wear tester, and the image analysis, etc. Al₂O₃+ZrO₂ composite coatings with different Al₂O₃ mixing ratio and thickness were compared in their corrosion resistance. The results showed that the higher alumina content and thicker coatings, the better the corrosion resistance, which was attributed to the diffusion resistance of corrosion reaction.