Temperature in the rearmost stabilization zone has an important impact on the final stabilization degree of PAN precursor fibers during industrial successive pre-oxidation and on their structure and properties. FTIR, X-ray diffraction, elemental analysis, ultramicrotomy and optical microscopy were used to study the slow evolution of stabilization indices and structure changes with increasing the temperature in the rearmost zone. The results show that cross linking reaction happens above 240 degrees C in the rearmost stabilization zone, leading to a quick increase of oxygen content and aromatization index and the formation of cross-linking rigid structure. Especially for the sample treated at 275 degrees C, the cross-linking structure induces a compact sheath layer in the fiber which impedes the oxygen atoms diffusion inward. By changing the temperature in the rearmost stabilization zone, the oxygen content, chemical structure and aromatization index can be accurately controlled.