Abstract: Friction stir welding is a new solid welding technique for aluminum alloys invented and patented by The Welding Institute,U.K.,in 1991.The objective of this paper was to schematically introduce the friction stir welding process and laid emphasis on the new development,which comprised of the research on FSW principles,that is,the behavior of plastic flow and the formation principle of onion rings,and the microstructure of friction stir welds,mechanical properties,welding tool,compound welding procedure,and the application fields of FSW.The paper also discussed the prospect of FSW.