In this paper we studal the UV-induced refractive index changes of a boron-codoped germanosilicatepreform usedfor foe fabrication of fiber gratings by use Of the color-center model. Two groups of performs, non H2loadedpreform and H2, loadedpreform, are exposed to UV beam of various pulse energy densities and pulse numbers.and their UV-induced excess losses are meosured. The corresponding refractive-index changes are determinedthrough a Kramers-Kroning analysis. Also, our experimental results are discussed and onalyzed according to thecolor-center model of photosensitivity and then some important conclusions are obtained. Two groups of perform, non-loaded preform and H2, loaded preform, are exposed to UV beam of each pulse energy densities and pulse numbers. and their UV-induced excess losses are meosured. The corresponding refractive-index changes are determined through a Kramers-Kroning analysis. Also, our experimental results are discussed and onalyzed according to the color-center model of photosensitivity and then some important conclusions are obtained.