The work aims to improve the oxidation resistance of C/C composites. SiC-Al2O3-SiO2 (SAS) composite coatings were prepared on the surface of C/C composites by atmospheric plasma spraying, and oxyacetylene test was proceeded at 1500 ℃ to evaluate the anti-ablation performance. XRD, SEM, EDX and other detection methods were used to detect the agglomerated powders, plasma spheroidized powders and the composition and structure of the coating before and after ablation. After plasma spheroidization, the fluidity of three powders was about 90 s/50 g. Compared with the agglomerated SiC-Al2O3-SiO2 powder, the powder fluidity was improved by about 20%, and the normal density was increased by 20%, which was more suitable for the APS process. The microstructure and compactness of the coating prepared by plasma spheroidized SiC-Al2O3-SiO2 powder were obviously better than those prepared by agglomerated powder. After ablation for 600 s at 1500 ℃, SiC- 36%Al2O3-4%SiO2 coating had the best anti-ablative effect in the group. The coating was intact and the mass ablation rate was 1.62×10?4 g/s. The SiC-Al2O3-SiO2 system solves the problem of low deposition rate and decomposition of SiC when preparing SiC coating by plasma spraying. SiC-Al2O3-SiO2 coating has good anti-oxidation ablation effect. SiO2 and Al2O3 form mullite phase during ablation, which has good high temperature stability, thermal shock resistance, low thermal expansion rate and oxygen diffusion, which can further improve the anti-oxidation ablation effect of the coating.