The pre-irradiation method is introduced to prepare methyl methacrylate graft-copolymerized composite separators. The morphologies of the grafted membranes (GMs) were observed under a scanning electron microscope. The cyclic voltammetry and electrochemical impedance spectra results indicated that the obtained polymer electrolytes (PEs) based on GMs could hold the excellent performance of Li + transportation and possess good affinity with Li metal electrode. The Li/PEs/LiCoO 2 cells demonstrated excellent cycling performance with little capacity loss after 80 cycles. These cells also showed a good rate property and could retain 70.2% (25°C) and 81% (75°C) of discharge capacity at 2C rate as compared to that at C/5 rate. The results of this paper suggest that the high-quality composite separators can be obtained by pre-irradiation technique, and this also offered a new and convenient way for the large-scale manufacture of Li-ion polymer battery.