Abstract: Polyetheretherketone (PEEK) composites have excellent impact resistance and thus have important potential application value in aviation field. However, the molding temperature of PEEK composites is too high for carbon fiber (CF) with epoxy sizing agent, which will result in the decomposition of sizing agent and further cause the reduction of interface strength and deterioration of load transfer. It will affect the application of PEEK composites. The effect of high-temperature gas-phase oxidation of CFs on the tensile and interlaminar shear properties of PEEK composites was systematically studied. CFs oxidized under different conditions were firstly prepared and characterized by XPS, inverse gas chromatography (IGC), bundle tensile testing to study the effect of oxidation on surface activity, surface energy and mechanical properties of CFs. The results show that appropriate oxidation conditions are beneficial to improving surface activity and surface energy of the CFs, while oxidation will decrease the tensile strength of CFs. CF/PEEK prepregs were prepared using the melt method, and the tensile properties and interlaminar shear properties of the composites were compared between untreated fibers and oxidized fibers. The results show that after oxidation, the 0° tensile strength decreases by more than 20%, indicating that high-temperature oxidation of CFs will cause fiber damage; The difference in 90° tensile strength does not exceed 10%, and the difference in interlaminar shear strength is less than 5%, indicating that the high-temperature oxidation of CFs failed to improve the interface properties of the composites. The above results show that adding the high-temperature oxidation process of CFs to the prepreg preparation process is not conducive to improve composite properties.