The invention discloses a sandwich type solid-state composite electrolyte membrane and a preparation method and application thereof, the electrolyte membrane is formed by permeating a composite electrolyte into a microporous diaphragm, and the composite electrolyte is composed of a high-molecular polymer material, a lithium salt and an ionic liquid. Or the electrolyte is composed of the inorganic solid electrolyte powder, the high-molecular polymer material, the lithium salt and the ionic liquid. The preparation method comprises the following steps: preparing raw materials into slurry, and coating two surfaces of the microporous diaphragm with the slurry. The electrolyte membrane disclosed by the invention has the advantages of relatively good thermal stability and electrochemical stability, relatively high ion transference number, ionic conductivity and safety, easiness in forming and processing, excellent mechanical property and the like, is a novel solid-state composite electrolyte membrane with excellent performance, and can be used for constructing a solid-state battery with high specific capacity, good cycling stability and good safety; the use value is high and the application prospect is good. The preparation method of the electrolyte membrane has the advantages of simple process, continuous production and the like, is suitable for large-scale preparation, and is convenient for industrial application.