In this paper, the factors affecting the refractive index distribution of graded index polymer preform, such as polymerization reaction temperature, concentration of dopant, molecular volume of dopant, refractive index of dopant., were discussed systematically. According to the relationship between the factors and the refractive index distribution of GI POF preform, high performance GI polymer preform was prepared by interfacial-gel polymerization technique, in which diphenyl sulfide was used as higher refractive index molecules (M-2), MMA was used as monomer (M-1), BPO was regarded as polymerization initiator, and n-LB was used as chain transfer agent.