Abstract: Microstructural changes of C/C composites after braking test were studied by TEM, RMS, SEM and so on. Microstructural model of worn surface layer was established. Temperature fields of specimens with asperities were simulated by Finite Element Method (FEM). The results show that a friction layer with several microns forms on the matrix firstly, and then a friction film covers on the friction layer unequally. TEM and SAED indicate that most fields of the friction film are middle textured, and the texture degree increases with approach to the worn surface. The outmost surface is highly graphitized, and this result is verified by RMS. The highest temperature of asperities is much higher than that of worn plane, which is one of the main factors of stress graphitization on worn surface.