TaB₂-SiC coating modified by different content of MoSi₂ was fabricated on graphite substrate with SiC inner coating by liquid phase sintering to elevate the anti-oxidation capability of the TaB₂-SiC coatings. As compared to the sample with the TaB₂-40wt%SiC coating, the coating sample modified with MoSi₂ exhibited a weight gain trend at lower temperatures, the fastest weight loss rate went down by 76%, and the relative oxygen permeability value reduced from about 1% to near 0. More importantly, the large amount of SiO₂ glass phase produced over the coating during oxidation was in contact with the modification of MoSi₂, which was proved to be beneficial to the dispersion of Ta-oxides. A concomitantly formed continuous Ta-Si-O-B compound glass layer showed excellent capacity to prevent oxygen penetration. However, when the TaB₂ content was sacrificed to increase the MoSi₂ content, the relative oxygen permeability of the coating increased instead of decreased. Thus, on the basis of ample TaB₂ content, increasing the MoSi₂ content of the coating is conducive to reducing the relative oxygen permeability of the coatings in a broad temperature region.