Polytetrafluoroethylene-co-hexafluoropropylene (FEP) films were irradiated in N,2, with ,60,Co γ-rays, and graft-copolymerization reaction was conducted after the irradiation with a bi-monomer system of acrylic acid (AA) and sodium styrene sulfonate (SSS) to prepare FEP−g−PSSA/AA membranes, which can be used as fluoro−sulphonic proton exchange membrane. Effects of the reaction conditions on grafting yield were studied in detail, such as the Cu (CH,3,COO),2,inhibitor concentration, the film thickness, mol ratio and total concentration of the monomers solution. The results showed that the grafting yields did not change with thickness of the FEP film samples, and with FEP films that had been kept under −5℃ after the irradiation for over three months.