In this study, we prepared a kind of composite solid polymer electrolyte (CSPE) based on montmorillonite (MMT) nano-clay fillers, lithium-bis(trifluoromethanelsulfonyl) (LiTFSI), polyvinylidenedifluoride (PVDF) and polyvinyl alcohol (PVA) copolymer by the casting method. Effect of the montmorillonite on ionic conductivity and electrochemical properties of the polymer electrolyte was demonstrated. The result CSPE obtained a higher ionic conductivity up to 4.31×10−4 Scm−1 at room temperature when 4.0wt% MMT was contained, and the maximum lithium ions transference number of 0.40 was achieved. Electrochemical performance of the polymer solid electrolyte was evaluated in Li/polymer electrolyte/LiFePO4 coin cell. Good performance with low capacity fading on charge–discharge cycling was achieved, indicating the potential application of the as-prepared CSPE in lithium ion batteries.