After irradiation of F2311 by γ ray (50—1000kGy) in vacuum, nitrogen and air, its average molecular weight, tensile strength and breaking elongation decreased as irradiation dose increased. But the gel fraction at first decreased and then increased with the increment of dose, on the dose of 750kGy the minimum value has been obtained. The changes of glass transition temperature and modulus are similar to that of the gel fraction. The IR analysis of sample indicated the formation of — CF=CH —, — FC=CF — and — C=O groups. Microstructures for irradiated samples were studied by SEM. Results showed that air promoted the irradiation degradation of F2311 and nitrogen inhibited that of it in a certain extent.