The controllable shunt reactor（CSR）is one of the key elements used in an extra-high voltage（EHV）/ultra-high voltage（UHV）transmission system for reactive power control.In contrast to conventional CSRs，EHV/UHV CSRs are at a higher voltage level and with a larger capacity，which makes higher requirements on the indices such as response speed，harmonic distortion，reliability and the corresponding techniques.An overview is made of domestic and foreign developments in four key techniques of EHV/UHV CSR，including body structure design，electromagnetic transient modeling，protection configuration research and control system design.The advantages and disadvantages of different technical schemes are discussed.Key issues of the four techniques are pointed out，and the trends in application and development are projected.