The invention discloses an inorganic-organic compound solid electrolyte, a preparation method thereof and an assembled all-solid-state lithium battery. The inorganic-organic compound solid electrolytecontains one or more of polymer binders, namely butadiene styrene rubber, nitrile rubber, polyacrylonitrile, silicone or derivatives thereof as well as lithium salt and inorganic nano-particles, wherein the mass percentage of the polymer binders in the electrolyte is 5%-60%, the mass percentage of the lithium salt in the electrolyte is 10%-80%, and the inorganic nano-particles in the electrolyteis 10%-40%. The inorganic-organic compound solid electrolyte has relatively high room-temperature ionic conductivity, relatively wide electrochemical windows and relatively good mechanical properties;by utilizing the provided preparation method of the compound solid electrolyte, a large-area solid-state electrolyte film is easily prepared; and the compound solid electrolyte has relatively high mechanical properties and excellent electrochemical stability, and the assembled battery has stable cycle performance and relatively high volume.