The invention provides a method for simply and conveniently preparing a large-size polymer electrolyte film for a lithium-ion battery, relates to a preparation method of a polymer electrolyte film for a lithium-ion battery, and mainly aims at solving the problems of liquid leakage and a potential safety hazard of an electrolyte and relatively low conductivity of an all-solid-state electrolyte film in an existing commercial battery. The preparation method comprises the following steps: dissolving 0.5g of PVdF into 2-3ml of DMF solvent for 15 hours, dissolving 2wt%-6wt% of MMT into 1-2ml of THF solvent for 15 hours, and further stirring the mixture for 15 hours after mixing; carrying out ultrasonic treatment on the stirred solution for 5-10 minutes, dissolving 0.1g of PVA into 1-2ml of DMF solvent for 2 hours, and further mixing with the solution mixed with the PVdF and the MMT; and adding a proper amount of lithium salt, further stirring the lithium salt for 6 hours, dumping the stirred polymer solution on a clean glass plate, putting the glass plate into a vacuum drying oven for drying treatment, carrying out heating at 120 DEG C for 60 minutes, and then taking out the product for later use. The method provided by the invention is applied to the field of the lithium-ion battery.