Abstract: Mechanical properties of domestic and overseas (T300) PAN-based carbon fibers are measured. Chemical composition, crystallite size parameter,surface and fracture texture of both carbon fibers are studied by chemical analysis, SEM observation and X-ray. The fracture texture characteristic graph of both T300 and domestic carbon fibers are presented. On the basis, effects of the fibers structure on the carbon fibers properties and relationship between the carbon fibers structure and thier properties are analysized.