We have investigated formation of Ge-related defects in a GeO2-SiO2 glass fiber preformed by poling with ArF laser excitation. Electric field dependence of the induced-defect concentrations was measured by means of the optical absorption. Several color centers such as the germanium electron-trapped centers and the Ge E′ center were induced. Concentrations of the induced germanium electron-trapped centers and Ge E′ center increase with increasing the electric field. Conversion efficiency from the germanium electron-trapped centers to the Ge E′ center was found to be independent of the electric field. The present result strongly suggests that the poling with ArF laser excitation is effective in the present GeO2-SiO2 glass for the formation of germanium electron-trapped centers.