Grafting copolymerization of mixture of acrylic acid (AA) and sodium styrene sulfonate (SSS) onto high density polyethylene (HDPE) membrane was studied by the mutual γ-irradiaton technique. At last we prepared a strong acid cation exchange membrane by one-step method. Sufficient amounts of AA groups could be grafted onto the surface of PE firstly and the hydrophilicity of the surface was improved. By studying the grafting of SSS and the mixture of AA and SSS onto PE, we found SSS could not graft onto PE without AA. In this article, grafting conditions as well as dose, the effects of monomers feed composition and total concentration of monomers were discussed. The mechanical and chemical properties of membranes were also tested.