In this article, an improved method was put forward to overcome the defect of interfacial-gel polymerization technique. The cause of the defects was analyzed, and the factors of reaction conditions on formation of the graded-index (GI) polymer preform (i.e., reaction temperature and atmosphere pressure) were investigated. High-performance large-sized GI polymer preform was prepared by this improved technique, in which diphenyl sulfide was used as higher refractive index molecules. (C) 2003 Wiley Periodicals, Inc.