A theoretical analysis was conducted on the preparation of gradient-index (GI) polymeric rods by a centrifugal field. Two kinds of materials system were used in this study: a polymer/monomer mixture and a polymer/dopant mixture. The predicted refractive index distribution (RID) was in good agreement with the experimental data reported in the literature. The effects of the essential parameters, including the molecular weight of the polymer, the composition and component properties (refractive index and density) of the mixture, the rotating speed, and the diameter of the GI rod on the RID were investigated. The results of a numerical simulation reveal that the essential parameters have significant effects on the RID. A materials property requirement was established theoretically for obtaining a rod RID with the refractive index decreasing from the center to the periphery. That is, the order of the density between the polymer and monomer (or dopant) needs to be the reverse of the refractive index. The enhancement of the polymer molecular weight, rotating speed, and rod radius increases the refractive index difference between the rod center and the periphery (bn). However, the optimization of these parameters is required to obtain a suitable RID for practical applications.