The preoxidizing process of polyacrylonitrile (PAN) fiber is investigated with in-situ X-ray diffraction techniques in this paper. Through experiment

we determined the curve of wide angles diffractering intensity. From the resolution charts which were gained of different times from the determination of PAN WAXD(wide-angle X-ray diffraction)

one can calculate the crystallinity

the microcrystalline sizes

the spacing of lattice and the "aromatization index" values for the samples. And all this

these parameters with transient case of the change of the experimental condition were discussed in detail. Simultaneously. the bethaviour of the cyclizatic kinetics during the processing of PAN fiber to preoxidized fiber was described. The rate constant of cyclization reaction and the activation parameter of cyclization at each temper-ature were calculated. The studies of these structural parameters and kinetics may provide some fundamental information for the optimizing control for the industrial process of the high-performance PAN-based arbon fibers.