A novel copolymer, poly(methyl methacrylate-acrylonitrile-butyl acrylate) [P(MMA-AN-BA)], was designed for high-safety and high voltage lithium ion battery in this paper. The copolymer was synthesized by emulsion polymerization, the corresponding membrane was prepared through phase inversion method and the gel polymer electrolytes (GPEs) were obtained by immersing the membranes into 1M LiPF6 liquid electrolyte. The performances of the copolymer, the membranes and its GPEs were characterized by Fourier transform infrared spectra, nuclear magnetic resonance spectra, scanning electron microscope, energy dispersive spectroscopy, Brunauer–Emmett–Teller, mechanical stability, differential scanning calorimetry, thermogravimetric analyzer, electrochemical impedance spectroscopy, cyclic voltammetry and charge/discharge test. The results show that the copolymer is obtained through opening the double bonds CC of its monomers. The mechanical strength and thermal stability of PE separator are promoted by coating the developed copolymer. The PE-supported and copolymer coated membranes exhibit homogeneous and interconnected pore structure, which helps to present the highest ionic conductivity of 1.70×10−3 Scm−1 for the corresponding GPE at room temperature. The GPE is electrochemically stable up 5V, and shows the acceptable cyclic and rate performance when used in LiNi0.5Mn1.5O4 cathode. The high performance of GPE assures the practical application of high voltage cathode in lithium ion battery.