Unified power flow controller in Suzhou 500 kV Southern Power Grid is the highest voltage class and largest capacity UPFC project in the world.It is used to solve the problems of uneven power flow distribution,over-limited sectional flow and poor dynamic reactive support ability,et al.The principle and protection configuration scheme of UPFC are summarized,and the action results of typical fault points are expounded in detail.The research of 500 kV UPFC in this paper provides a reference for the study of the protection of the flexible transmission system with higher voltage levels in future.