The tests of thermal shock and static oxidation are done to C / C composite coating processed through soaking, coat brushing and solidifying. Then the coating's anti-oxidation and mechanism invalidity are discussed through the contrast and study by using SEM and TGM. The result shows that microcracks in the coating are the main cause for coating invalidity, so the thickness of C / C composite coated on the brake should be selected within 0.03 to 0.05 mm.