Abstract: According to unidirectional C/C composites prepared by CVI,thermal mechanism and the effect of the fiber content on thermal conductivity coefficient of C/C composite were investigated.The results show that the thermal conductivity (TC) coefficient parallel to the fiber direction is 10 times larger than that perpendicular to the fiber direction.The parallel thermal conductivity coefficients enhance with the increase of carbon fibers at all different temperature of HTT,while the perpendicular TC coefficients enhance with the increase of carbon fibers only at low temperature of HTT and they firstly enhance and then decrease at high temperature of HTT.