Abstract: With the development of fast reactor technology in China, the traditional post-processing technology is particularly insufficient in the process of disposing of spent fuel, and it is urgent to develop a new reprocessing process. Therefore, a dry reprocessing technology that can perform spent fuel reprocessing in a high-temperature and anhydrous environment was widely studied. High-density graphite (HDG) is considered to be one of the most promising crucible candidate materials due to its excellent thermal shock resistance and high-temperature strength. However, in the process of treating spent fuel by molten salt electrolysis, a high-density graphite crucible will directly in contact with corrosive media such as high-temperature chloride molten salt and spent fuel, which will cause corrosion to the crucible and affect the stability and service life of the crucible. Plasma-sprayed yttrium stabilized zirconia (YSZ) coating on the crucible surface was proven to have excellent properties, but the defects such as holes, cracks, and droplets in the coating will seriously restrict the performance of YSZ coating at high-temperature. Therefore, it is particularly urgent to improve the density of the YSZ coating by the sealing treatment. In this paper, an Al₂O₃ overlay was prepared on the surface of the YSZ coating by magnetron sputtering (PVD) method and metal-organic decomposition (MOD) method. The effects of the Al₂O₃ overlay prepared by these two methods on the corrosion resistance of YSZ coating in NaCl-KCl molten salt were studied. The morphology and microstructure of the coatings before and after the corrosion test were characterized by SEM, EDS, and XRD. The results show that the Al₂O₃ overlay prepared by PVD method is mainly distributed on the surface of the YSZ coating. The surface density of the YSZ coating is improved to some extent, but the internal density and corrosion resistance of the coating are not significantly improved. The overlay prepared by MOD method can effectively fill the defects on the surface of YSZ coatings, such as cracks and holes. At the same time, the inherent wettability of MOD precursor solution makes it easy for the precursor to penetrate the YSZ coating, thus effectively filling the internal defects of YSZ coating to improve the coating density. The overlay resistance of the YSZ coating with the Al₂O₃ overlay prepared by the MOD method is significantly improved, and the presence of the Al₂O₃ overlay also effectively reduces the consumption of the internal stabilizer.