A novel composite polymer electrolyte was prepared by blending an appropriate amount of LiClO₄ and 10% (mass fraction)fumed SiO₂ with the block copolymer of poly (ethylene oxide) (PEO) synthesized by poly (ethylene glycol) (PEG) 400 and CH₂Cl₂.The ionic conductivity, electrochemical stability, interfacial characteristic and thermal behavior of the composite polymer electrolytewere studied by the measurements of AC impedance spectroscopy, linear sweep voltammetry and differential scanning calorimetry(DSC), respectively. The glass transition temperature acts as a function of salt concentration, which increases with the LiClO₄ content.Lewis acid-base model interaction mechanism was introduced to interpret the interactive relation between the filled fumed SiO₂ andthe lithium salt in the composite polymer electrolyte. Over the salt concentration range and the measured temperature, the maximumionic conductivity of the composite polymer electrolyte (10^-4.41 S/cm) appeared at EO/Li=25 (mole ratio) and 30℃, and the begin-ning oxidative degradation potential versus Li beyond 5 V.