The damage of different carbon fibers was studied from high temperature, infiltration and pyrolysis of Polycarbosilane (PCS), and the oxygen in PCS. The result shows that the graphitizing extent and surface status influence the damage of carbon fiber greatly. The carbon fiber M40JB with a higher graphitizing extent was damaged more seriously; the carbon fiber JC1# with an active surface was sensitive to the variation of outside condition; however, the carbon fiber JC2#, which had a lower graphitizing extent and not active surface, was damaged less and was more stable.