Abstract: Glass Fiber Reinforced Plastic (GFRP) is used as spare materials for the supporting flange of the BES III beam pipe in the Beijing Electron Positron Collimator(BEPCII) because of its excellent electrical insulating performance and mechanical properties. However, during the BEPC II operation, the beam pipe suffers a significant amount of γ and neutron irradiation. When GFRP is exposed to γ irradiation, the material will become damaged, and its mechanical properties will vary. The tennsion-tension fatigue properties of GFRP laminated sheets before and after 20 kGy, 100 kGy, 200 kGy γ irradiation were studied. The results show that the effect of γ irradiation on the fatigue life in the low-cycle fatigue range is obvious, but it has little impact on the high cycle fatigue range. Based on the hypothesis of fatigue proposed by Hwang and Han, a two parameter fatigue life model was establishied. The microstructure of GFRP laminated sheets before and after γ irradiation were observed by SEM. The images show the glass fiber doesn't change obviously, but the epoxy degrades to pieces after irradiation. FTIR spectra indicate that the degradation reaction predominates over the crosslinking reaction of epoxy after γ irradiation.