The nature of photosensitive defects in germania doped silica glasses under irradiation of 488 nm Argon laser and 193 nm ArF excimer laser are investigated. From the careful measurement of UV induced absorption bands, photoluminescence changes, and electron spin resonance (ESR) experiments, we found that the 5.1 eV germania defect absorption band in fibers is composed of 5.06 eV photo bleachable band and 5.17 eV relative photochemically stable band. And the photoluminescence at 295 nm corresponding to 5.06 eV defects is decaying with 5.06 eV photobleaching. While the luminescence at 395 nm is attributed to 5.17 eV defect and its intensity keeps constant with UV irradiation. The structural models of two defects are presented, the bleaching dynamic of absorption with laser irradiation is analyzed, and the photosensitive processes with different laser sources are discussed.