Four kinds of phenyl silicone resin with PhSiO3/2, MePhSiO2/2, and SiO4/2 unit were prepared through hydrolysis-condensation reaction, and the phenyl group content was determined by ultraviolet absorption spectrophotometry at 263 nm, and the relationship between the phenyl content and the reflective index was studied. The results showed that the reflective index of the phenyl silicone resin was mainly related with the content of phenyl group, and had little relation with the content of other groups such as methyl and vinyl group. Ignored the effect of other groups relationship between the reflective index of the phenyl silicone resin and the phenyl content agreed with the following formula： nD = 1. 419 94 ＋ 0. 021 08M （Ph）.