Gel polymer electrolyte (GPE) is able to solve the problem of poor cyclability for high voltage cathode such as LiNi0.5Mn1.5O4 at elevated temperature to some extent, but the traditional GPE based on poly(vinylidene fluoride-co-hexafluoropropene) [P(VdF-HFP)] cannot meet the requirements in terms of ionic conductivity and electrochemical stability. A novel GPE, based on polyethylene-supported poly(methyl methacrylate-butyl acrylate-acrylonitrile-styrene) (P(MMA-BA-AN-St)/PE), is reported in this paper. Physical characterizations indicate that the polymer membrane has a better pore structure and higher electrolyte uptake, leading to the improved ionic conductivity of 2.7×10−3 Scm−1 at 25°C for resulting GPE. Electrochemical characterizations show that the developed GPE exhibits lower interfacial resistance with lithium electrode and higher oxidative decomposition potential (up to 5.3V, vs. Li/Li+). In addition, LiNi0.5Mn1.5O4 cathode shows excellent cyclic stability under 55°C at 0.2C between 3V and 4.9V, in which the capacity retention of cathode combined with GPE is 81% after 150 cycles, compared with only 25% when using a liquid electrolyte.