Abstract: At present, the thermal protection mechanism of SiC-based materials for hypersonic vehicles mainly depends on the SiO₂ protective layer formed by SiC passive oxidation at 1200-1700℃. However, the high-tempera-ture gas effect caused by hypersonic flight makes the thermal protection materials subjected to high temperature, low pressure and atomic oxygen loadings. The high activity of atomic oxygen will change the type of SiC oxidation reaction, resulting in the loss of protective ability. Therefore, the identification of active and passive oxidation types of materials under different flight conditions will directly determine the use threshold of materials, which is very important for the thermal protection systems (TPS) design of hypersonic vehicles and the development of new thermal protection materials. Based on it, this paper breaks the traditional method of analyzing the micro-composition of materials after oxidation, and establishes an on-line identification method and system of active and passive oxidation reaction for SiC-based thermal protection materials under high temperature, low pressure and atomic oxygen environment based on spectral diagnosis radio frequency (RF) plasma discharge and high power laser technology. The rapid on-line identification of active and passive oxidation reaction for SiC-based thermal protection materials is realized. After material analysis by SEM, EDS and XRD, the accuracy and reliability of this method were verified, and the evolution law for active oxidation of SiC materials in atomic oxygen environment was further explored, which provides an important support for the protection threshold of SiC-based thermal protection materials and the improvement of material properties.