The composite membrane of glass microfiber and polyimide was prepared by paper making method and following dip-coating process to explore the feasibility as high performance separator of lithium ion battery (LIB). It was demonstrated that the composite membranes, with a thickness of about 45μm, possessed a significantly enhanced tensile strength and a modified porous structure, compared with that of pristine glass microfiber membrane. Impressive improvements in thermostability and flame retarding were achieved for composite membrane, with no shrinkage at the elevated temperature of 200°C, even no burn on fire, compared with commercial polyolefin separators. Meanwhile, the composite membrane presented a favorable wettability and remarkable electrochemical stability in commercial liquid electrolyte. In addition, the battery test results of LiFePO4/Li and LiFePO4/graphite cells proved the composite membrane was a promising separator with an improved rate capability. The cycle performance of cells at the elevated temperature of 120°C demonstrated their excellent safety characteristic as separator in LIB, indicating the composite membrane was a potential separator candidate for high power battery.