An automated multiple-beam Fizeau fringes in transmission technique was used with a fiber-drawing device to detect necking deformation along polypropylene (PP) fibers axis under different conditions of annealing process. The refractive indices, refractive index profiles and crystallinity were calculated along the annealed PP fibers at different draw ratios. The annealing temperature controls the propagation of necking deformation along PP fibers axis that stretched at low draw ratios(D< 2). The necking deformations along PP fibersaxis due to fast drawing process could be avoided when PP fibers were annealed at the temperature of 120oC. Microinterferograms are given for illustrations.