Abstract: The aromatization index(AI),cyclization index(CI),relative cyclization index(RCI) and density of PAN fibers were studied by X-ray diffraction(XRD),differential scanning calorimetry(DSC),Fourier transform infrared spectroscopy(FT-IR) and thermogravimetry coupled with mass spectroscopy(TG-MS).The veracity and applicability of the four evaluation methods on preoxidation extent of PAN fibers were also compared.The results showed that CI and RCI were more suitable to evaluate the preoxidation extent at initial stage of preoxidation process,while AI was suitable at middle and later stage.Density could be used to evaluate the preoxidation extent at the whole preoxidation process.