HfC-SiC modified C/C composites containing in situ formed Si-HfC-HfSi₂ ablation resistant layer and SiC oxidation resistant layer were successfully prepared by reactive melt infiltration (RMI) combined with gaseous silicon infiltration (GSI). A comparative study was conducted on the anti-oxidation and anti-ablation performance of the C/C-HfC-SiC composites with GSI (noted as RG-CHS) and without GSI (noted as R-CHS). After oxidation at 1,500 ℃ for 200 min, the oxide film of RG-CHS remained intact. The mass and linear ablation rates decreased from 1.31 mg/s and 7.36 μm/s to 0.12 mg/s and −0.22 μm/s after GSI process, respectively. The introduction of low melting point phases and reducing surface defects can improve the high temperature oxidation resistance and plasma ablation resistance of the composites.