The pseudo-graphite crystalline structure of carbon fiber is the origin of its excellent mechanical properties. The formation and evolution of crystalline structure of PAN stabilized fiber during carbonization were investigated by the method of wide angle X-ray diffraction in present. The results indicated that : below 1000℃

the polycyclic aromatic structures

which were generated during stabilization process

were closed together and packed parallel to the fiber axis just like nucleation judged by the phenomenon that the d spacing of (002) miller plane was decreased while the crystallites grow slowly. When the heat treatment temperature is higher than 1000℃

the crystallite sizes were increased obviously

implied the three dimensional growth of the pseudo-graphite crystalline structure. During the graphitization stage when the heat treatment temperature was above 1500℃

the crystallite sizes were increased rapidly due to the rearrangement of the crystalline structure. According to the presented results

the structural design and adjustment could be achieved by controlling both the rate of nucleation and growth for pseudo-graphite crystallites.