Compared with conventional organic liquid electrolyte batteries, all-solid-state batteries for next-generation energy storage have attracted recent attention due to their advantages of high safety, high energy density and long cycle life. Organic-inorganic composite solid electrolytes as the most promising electrolyte systems have some advantages of inorganic solid electrolytes with a high strength, a high stability and a high ionic conductivity, and some advantages of solid polymer electrolytes for softness and easy processing as well. This review introduced the fundamentals of Li-ion solid-state electrolytes, and discussed some problems of organic-inorganic composite solid electrolytes (i.e., ionic conductivity, solid-solid interface, electrochemical window and compatibility between organic and inorganic compounds) and optimization strategies. In addition, some challenges and future development on organic-inorganic composite solid electrolytes were also described.