The invention discloses a composite solid electrolyte membrane as well as a preparation method and application thereof. The preparation method of the composite solid electrolyte membrane comprises thefollowing steps: (1) mixing an organic solvent and a binder to obtain a mixed glue solution; (2) mixing the mixed glue solution with sulfide electrolyte to prepare slurry so as to obtain mixed slurry; and (3) forming the mixed slurry on at least one part of the base membrane to obtain the composite solid electrolyte membrane. In the step (1), the organic solvent is selected from at least one of dichloromethane, tetrahydrofuran, n-hexane, n-heptane, methylbenzene, 2,4-dimethyl-3-pentanone, chlorobenzene, xylene, anisole, cyclohexanone, and 1,3,5-trimethylbenzene, n-decane and methyl formamide.The composite solid electrolyte membrane obtained by the method disclosed by the invention has the advantages of good flexibility, high strength, good toughness, high ionic conductivity and good thermal stability.