Abstract: SiC coatings were prepared successfully on graphite crucible slices surface by in-situ reaction method and cyclic thermal oxidation experiments of the coatings were performed . The formation mechanism of SiC coating and the effects of sintering temperature and time on the thickness of the coatings were studied, and the roles of the coating in improving thermal oxidation resistance and thermal shock resistance were also evaluated. The results show that the thickness of SiC coatings prepared by in-situ reaction method was uniform. The in-situ reactions at different temperatures were controlled by different kinetic processes. When the temperature was very close to the melting point of silicon, long heating time could significantly increase the thickness of SiC coatings, and the higher the sintering temperature, the larger the thickness of the coating. SiC coatings on graphite surface could greatly improve the thermal oxidation resistance and thermal shock resistance of the graphite matrix, and the improvement was more significant with the greater coating thickness.