Abstract: Existing hydropower stations mostly adopt the constant-speed generation systems, which will not only cause a decrease in periodic hydro-energy capture efficiency but also deteriorate the unit operation environment. The variable-speed operation（VSO）of the hydraulic turbine is the key to overcome the above-mentioned drawbacks. This paper reviews the application and development of the variable-speed constant-frequency（VSCF） technology in the hydropower generation field. Firstly, the common types of hydropower stations and the principles of constant-speed generation systems are described, and the advantages and disadvantages of VSO systems are induced. Then, the main realization methods and operating principles of the VSCF technology are introduced; the characteristics and differences of each VSO system are compared; and the applicability and prospect of each system are analyzed. Finally, the emphases and difficulties of VSCF hydropower generation technologies are analyzed, and the future development trends are prospected.