A brief introductionof the hypersonic airbreathing propulsion system is first given,followed by a descriptions of working principles and compositionof typical hypersonic airbreathing engines, including scramjet,detonation engine and combined cycle engines. In the third part,the key difficulties encountered in developing these engines arepresented together with relevant key technologies, such as conceptdesign, inlet, combustor, nozzle, heat protection, light structureand fuel fedding/controlling. The main projects of hypersonicairbreathing propulsion system and the advancement achieved arereviewed in the fourth part, as well as lesson learned anddeveloping trends. The fifth part is focused on the combustionprocess and the mechanisms in these engines, where a survey onrelated research works is given.