A novel strategy, herein, is demonstrated for improving comprehensive properties of poly (methyl methacrylate)(PMMA)-based gel polymer electrolyte (GPE) with a core-shell PMMA-grafted ordered mesoporous silica (OMS-g-PMMA). The OMS-g-PMMA was synthesized by surface-initiated atom transfer radical polymerization of methyl methacrylate from the exterior surface of OMS particle. A series of PMMA-based GPE membrances, filled with the OMS-g-PMMA of different contents, were further prepared by solution casting technique. The OMS-g-PMMA was confirmed to possess regular core-shell structure, in which a PMMA shell is chemically grafted to the exterior surface of silica core remaining intact mesoporous characteristics. Compared to the bare OMS, the OMS-g-PMMA is found to more effectively improve the comprehensive properties of PMMA-based GPE including ionic conductivity, thermal stability, and mechanical properties as well. For the PMMA-based GPE filled with 15 phr OMS-g-PMMA, the ionic conductivity at 25°C reaches 1.59 × 10−4 S·cm−1, which is higher by nearly two orders than that of the corresponding filler-free parent GPE. Meanwhile, the tensile strength and Young's modulus increase by 2.39 and 2.41 times, respectively, with an improvement in glass-transition temperature () about 10°C. The excellent comprehensive properties make the PMMA-based GPE filled with OMS-g-PMMA as potential candidate for electrochemical devices.