NOVELTY - An all-solid-state polymer electrolyte film contains polyvinyl alcohol or its formal acid or homologs, boric acid, oxalic acid, and lithium salt which are dissolved gradually in organic solvent system to form polyvinyl-acetal-based chain, monolithium borate oxalate in the graft polymer chain.    USE - An all-solid-state polymer electrolyte film for solid-state lithium-ion polymer battery (claimed).    ADVANTAGE - The film has excellent film-forming ability, heat resistance, thermal stability, high mechanical strength, good water resistance, and stable chemical structure and circulation performance, operation process is simple, and safety performance of the lithium ion battery is effectively improved.    DETAILED DESCRIPTION - An all-solid-state polymer electrolyte film contains polyvinyl alcohol or its formal acid or homologs, boric acid, oxalic acid, and lithium salt which are dissolved gradually in organic solvent system to form polyvinyl-acetal-based chain, monolithium borate oxalate in the graft polymer chain having chemical crosslinking structure of formula (I).    R=H or 1-13C aliphatic or aromatic acetal or hemiacetal compound.    INDEPENDENT CLAIMS are included for:    (1) preparation of all-solid-state polymer electrolyte film which involves mixing polyvinyl alcohol or its formal acid or homolog in organic solvent according to ratio of 1:5-1:20 to obtain homogeneous solution, adding boric acid to homogeneous solution with molar ratio of polyvinyl alcohol or its formal acid or homolog and boron of boric acid being 0.5:1-5:1, dissolving while stirring at 50-90 degrees C, adding oxalic acid and lithium salt to homogeneous solution in which molar ratio of oxalic acid:boron atom:lithium salt is 2:1:2, dissolving while stirring at 70-120 degrees C, preparing into coating solution, and drying; and    (2) preparation of solid-state lithium ion battery which involves using all-solid-state polymer electrolyte thin film without using liquid electrolyte in which mechanical strength is 20-40 MPa, electrochemical stable window vs. Li/Li+ is 2-7 V, and ion conductivity is 10-6-10-4 S/cm.    DESCRIPTION OF DRAWING(S) - The drawing shows a microtopographic image of a polymer electrolyte film containing boric acid, oxalic acid, lithium carbonate, and polyvinyl alcohol by crosslinking treatment.