Composite polymer electrolyte is one of the most promising electrolyte candidates for future solid state lithium batteries, but inorganic fillers used are prone to an agglomeration, thus being difficult to form a continuous ion transport pathway. Flexible SiO₂ nanofiber porous membranes were fabricated by an electrospinning technique and a heating treatment process. The samples were characterized by scanning electron microscope, fourier transform infrared spectrometer, X-ray diffractometer, and thermogravimetry analyzer. The effects of TEOS proportion and polymer concentration in electrospinning precursor on the morphology and flexibility of the nanofiber porous membranes were investigated. Moreover, the electrochemical properties of PEO based composite polymer electrolyte (CPE-SiO₂) were analyzed. The ionic conductivity of this composite electrolyte can reach 2.52×10^–5 S/cm at 30 ℃. LiFePO₄|CPE-SiO₂|Li can be steadily charged/discharged for 50 times at 1 C rate and 60 ℃. Li|CPE-SiO₂|Li symmetric cell can keep a stable overpotential profile for 300 h with a low hysteresis at 60 ℃. This work provides an effective approach for the commercialization of next generation high-performance all-solid-state batteries.