A new technology in the field of power System，the Flexible AC Transmission System(FACTS), is gaining heeds of more and more electrical power technicians in the world due to its enormous advantages This paper gives a general overview of its development. briefly describes its devices and explainS its effects Furthermore, because of the tremendous influences on the power system bV the introduction of FACTS, there is a great demand to improve the power system analysis Also，this paper presents some aspects and directions needed to be studied.