The process of preparing SiC coating by electron beam-physical vapor deposition (EB-PVD)was discussed from viewpoint of thermodynamis.Results show that within the temperature range of 2 700-3 300 K,the ratio of SiC in the SiC coating doesn\'t change much and keeps around 0.7. Purity of the as-deposited SiC coating is not high.To improve the purity of the SiC coating,the SiC ingot is required to not be,necessary in full density but be fine-grained.