Around the near-infrared wavelength at which optical fiber gyroscope works, the effects of 120 krad γ-irradiation on single-mode quartz fiber are studied experimentally from the following several aspects: return loss, polarization dependent loss, scattering loss, absorption loss, mode field distribution and guided-mode propagation constants. The gap defect energy level and its increment are estimated from near-infrared spectroscopy and stimulated raman scattering experiment. The medium density change is studied by x-ray diffraction. The photothermal effect of irradiated fiber with γ-ray is observed by a high sensitivity interference circuit. The test data show that the UV anneal has some repairing effect, revealing the possibility that UV annealing method can serve as a mannes of active reinforcement.