A copolymer, polyacrylonitrile–methyl methacrylate P(AN–MMA), was synthesized by suspension polymerization with acrylonitrile (AN) and methyl methacrylate (MMA) as monomers. With this copolymer, polymer membrane was prepared by phase inversion. The performances of the polymer were characterized by FTIR, SEM, DSC/TG, EIS and LSV. The copolymer contains CH2, CN and CO bonds, and shows its thermal stability up to 300°C. The polymer membrane has a porous structure with an average pore diameter of 0.5μm. The conductivity of the polymer electrolyte is 1.25mScm−1 at room temperature, and it is electrochemically stable up to 5V (vs. Li). Using the polymer electrolyte as the gel polymer electrolyte (GPE), the cell Li/GPE/LiCoO2 shows its cyclic stability as good as the cell with liquid electrolyte.