Abstract: The surface character, microstructure, and surface chemical composition of PAN-based carbon fibers were investigated by SEM , WAXRD，SAXS, XPS and Raman spectroscopy. The relation between microstructure and mechanical properties was analyzed. Results show that with increase of heat treatment temperature from 2400 to 3000℃, tensile strength decreases, Young’  s modulus increases and the surface activity decreases. It is found that the interlayer spacing d002 decreases, both La and Lc increase，the crystallinity increases, the size of the pores and the volume percentage of large pores all increase, and the surface O/C atom ratio decreases after the heat treatment.