The invention relates to the field of lithium ion batteries, in particular to a polymer electrolyte membrane, a preparation method thereof and a lithium ion battery. The polymer electrolyte membrane contains a polymer matrix, lithium salt dispersed in the polymer matrix and polymer fibers, wherein the polymer fibers are provided by polymer fibers modified by a first silane coupling agent, and thefirst silane coupling agent is a silane coupling agent containing carbon-carbon unsaturated double bonds. The polymer matrix contains a cross-linked structure provided by a cross-linking agent, a copolymer chain structure provided by a cross-linkable copolymer, and inorganic nanoparticles. The polymer electrolyte membrane provided by the invention has the advantages of higher ionic conductivity, lower degree of crystallinity, proper flexibility, simple preparation method and process and lower cost.