Carbon/carbon (C/C) composites have shown great scope as thermal structural materials in the aerospace industry. However, the material is restricted from being applied in oxygen-containing airflow with high temperatures and high mechanical stress due to high-temperature oxidation. In this study, the ZrB₂-SiC-La₂O₃ coatings with different La₂O₃ contents were prepared on the surface of SiC-coated C/C composites by atmospheric plasma spraying technology. Focusing on the phase and morphology evolution, the oxidation behavior of the composite coatings at 1500 °C for 10 h was studied, which will guide the future application of ultra-high temperature ceramics coatings on C/C composites. The results showed that the composite coating with 10 wt% La₂O₃ displayed better oxidation resistance. The morphology of the coating after oxidation showed that La atoms partly substitute Zr atoms to form the high-temperature stable phase (La_0.1Zr_0.9)O_1.95 and Zr(La)-O-C compounds. These phases not only restrained the ZrO₂ phase transformation but also formed a dense barrier with the uniformly distributed molten phase to resist oxygen erosion, providing effective high-temperature protection for C/C composites. Nevertheless, the excessive addition of La₂O₃ destroyed the viscosity of the melt phase, which further reduced the high-temperature stability of the oxide layer.