This review discusses the development of sulfide-based composite solid electrolyte films for all-solid-state batteries (ASSBs). Sulfide electrolytes are favored for their high ionic conductivity and low-temperature processing, but traditional methods for producing thin films are challenging. A polymer-based composite electrolyte film offers a flexible, thin alternative with high ionic conductivity. The review covers the ionic transport mechanism, preparation methods, and properties of sulfide-based composite electrolytes, as well as their application in ASSBs. It also provides a perspective on future development directions. Sulfide-based composite electrolytes are promising due to their high ionic conductivity and compatibility with lithium metal anodes. However, challenges remain in achieving high conductivity and thin films. Various preparation methods, including wet and dry processes, are discussed, with wet methods like tape casting and infiltration being more effective for producing thin, high-conductivity films. The dry process, while energy-efficient, faces challenges in binder selection and compatibility with lithium metal. The review highlights the importance of optimizing binder selection, improving ionic conductivity, and developing new electrolyte systems. It also discusses the application of composite electrolyte films in ASSBs, including their performance in lithium symmetric cells and full cells. The development of composite electrolyte films is crucial for achieving high energy density and safety in ASSBs. Future research should focus on improving the mechanical properties, flexibility, and thermal stability of composite electrolyte films, as well as developing new binders and electrolyte systems that enhance performance and compatibility with lithium metal anodes.This review discusses the development of sulfide-based composite solid electrolyte films for all-solid-state batteries (ASSBs). Sulfide electrolytes are favored for their high ionic conductivity and low-temperature processing, but traditional methods for producing thin films are challenging. A polymer-based composite electrolyte film offers a flexible, thin alternative with high ionic conductivity. The review covers the ionic transport mechanism, preparation methods, and properties of sulfide-based composite electrolytes, as well as their application in ASSBs. It also provides a perspective on future development directions. Sulfide-based composite electrolytes are promising due to their high ionic conductivity and compatibility with lithium metal anodes. However, challenges remain in achieving high conductivity and thin films. Various preparation methods, including wet and dry processes, are discussed, with wet methods like tape casting and infiltration being more effective for producing thin, high-conductivity films. The dry process, while energy-efficient, faces challenges in binder selection and compatibility with lithium metal. The review highlights the importance of optimizing binder selection, improving ionic conductivity, and developing new electrolyte systems. It also discusses the application of composite electrolyte films in ASSBs, including their performance in lithium symmetric cells and full cells. The development of composite electrolyte films is crucial for achieving high energy density and safety in ASSBs. Future research should focus on improving the mechanical properties, flexibility, and thermal stability of composite electrolyte films, as well as developing new binders and electrolyte systems that enhance performance and compatibility with lithium metal anodes.