Unified power flow controller (UPFC), static synchronous series compensator (SSSC),thyristor controlled series compensation (TCSC) and phase shifter (PST) can be able to adjust line parameters and flexibly control power flow. They have been applied in domestic and foreign power grids,and have played an important role in balancing power flow in transmission channels and improving power supply capacity. The theoretical research and engineering practice of UPFC,SSSC,TCSC and PST are summarized. Firstly,the basic structure and power flow control principle of four kinds of power flow control devices are analyzed,and projections of power flow control devices are introduced. Then,the key technologies of power flow control devices are summarized from five aspects:topology,converter technology,location and capacity,control strategy and fault protection. Finally,the typical application scenarios of power flow control devices in the future power grid are prospected,and the research direction of power flow control technology in the future is analyzed.