In order to determine the development of the radial heterogeneity of oxidative polyacrylonitrile fibers，it is urgent to develop a detection method for the evaluation of homogeneous oxidation of polyacrylonitrile fiber.In this paper，fiber samples are prepared by resin embedding and polishing technique for optical analysis.The evolution process of the radial heterogeneity of two kinds of oxidative polyacrylonitrile fibers were compared and analyzed by optical microscope.The evolution model was proposed for the radial heterogeneity of oxidative polyacrylonitrile fibers.The results proved that typical radial heterogeneity is present in TG300 oxidative polyacrylonitrile fibers.However，no obvious radial heterogeneity is found in TG800 oxidative polyacrylonitrile fibers.When the oxidation reaction proceed，the diameter and carbon content of fiber decrease and the oxygen content increase gradually.Therefore， the optical microscope can be applied in the evaluation of homogeneous oxidation of polyacrylonitrile fiber.A new detection method is provided for the manufacture of homogeneous oxidative polyacrylonitrile fibers.