Abstract: UHV step controllable shunt reactor (SCSR) is mainly used in large-scale new energy transmission channel, to maintain the reactive power balance and voltage stability of UHV system, the high performance of protection is required. UHV SCSR includes grid windings and control windings, and auxiliary reactors connected to the control windings. The protection of UHV SCSR is complex compared to normal reactor. The protection configuration is researched based on electrical structure of UHV SCSR in ZhangBei~XiongAn project, and the solution of problems is proposed according to the result of dynamic test and the practical application in project. The protection configuration and matters needing attention of grid windings and control windings is introduced. The fixed capacity reactor instead of one phase of SCSR, the effect to the protection is analysed.