As an ideal propulsion system for hypersonic flight in near space and wide speed range and large airspace flight of aerospace vehicles， the combined propulsion system has high aviation and aerospace application value. Based on the analysis of the current combined propulsion schemes in the United States， this paper makes a preliminary discussion and estimate on its technical development and trend. The potential military applications are analyzed by taking several typical combined power aircraft as examples. Some suggestions for the development of combined propulsion system in China are proposed.