The cross-linked composite polymer electrolytes composed of poly(ethylene oxide) (PEO), hyperbranched polymer with terminal acryloyl groups (poly-1b), poly(ethylene glycol) methyl ether methacrylate (PEOMA), LiN(CF3SO2)2 were prepared, and their ionic conductivities, mechanical strength, electrochemical and thermal properties, and interfacial stabilities with electrodes were investigated. The ionic conductivity increased with an increase in the PEOMA content in the cross-linked composite polymer electrolyte, and the highest ionic conductivity was obtained at the [80% PEO/20% (poly-1b/PEOMA)]12(LiN(CF3SO2)2) electrolyte with the poly-1b/PEOMA ratio of 1/3. However, the tensile strength decreased with an increase in the PEOMA content in the cross-linked composite polymer electrolytes. The cross-linked composite polymer electrolyte with the highest ionic conductivity has three times higher tensile strength than non-cross-linked (80% PEO/20% poly-1a)12(LiN(CF3SO2)2) electrolyte. The addition of the PEOMA unit into the cross-linked composite polymer electrolyte improved both the ionic conductivity and mechanical property at the same time. And also, the cross-linked composite polymer electrolyte containing the PEOMA unit showed the good interfacial stability with both lithium metal and cathode electrodes.