In this study, Cr₂O₃ was applied to the surface of Al₂O₃ ceramic via a dip-coating method. Subsequently, the final coated ceramic was obtained through high-temperature sintering. The effects of the Cr₂O₃ coating on material composition, microstructure, secondary electron emission coefficient, surface resistivity, and vacuum surface hold-off voltage performance were systematically investigated. The results indicate that the surface of the coated ceramic appears dark red, representing a mixture of three materials: Al₂O₃-Cr₂O₃ solid solution, MgAl₂O₄, and Cr₂O₃. Compared to the Al₂O₃ ceramic, both the grain size and pore size on the surface are reduced, and the homogeneity of the grain size is significantly enhanced. After high-temperature sintering, Al and Cr diffuse into each other. Additionally, a small amount of glass phase, likely migrating from the ceramic substrate, is detected in the coating. Owing to the high-temperature sintering of the Cr₂O₃ coating, the secondary electron emission coefficient is reduced to 3.22, and the surface resistivity is also lowered to 4.52×10¹¹ Ω. Furthermore, the vacuum surface hold-off electric field strength of the coated ceramic increases to 34.44 kV/cm, which is approximately 108% higher than that of the Al₂O₃ ceramic.