Abstract: The thermal conductivity of six kinds of polyacrylonitrile (PAN) - based carbon fiber(CF)with different strength and modulus was measured by laser flash method. The effect of the thickness of CF samples and the test temperature on the CF axial thermal conductivity was studied. The crystallite size, orientation and order degree of CF were measured by X-ray diffraction (XRD) and Raman spectroscopy. The relationship between the thermal conductivity of CF and its microstructure was investigated. The results show that the thickness of the PAN-based CF sample has a slight effect on the thermal conductivity test, and the thermal conductivity decreases with the increase of the test temperature. The compactness, crystal size and structural order of the PAN-based CF have a greater impact on its thermal conductivity.