Abstract: With the increasing utilization of wind power, it becomes more and more important for wind plants to provide ancillary services including active power control and frequency regulation, which are usually required for conventional generators. This paper introduced the grid codes or technical requirements for wind plants or farms in frequency regulation or reserve allocation in some countries/regions. The frequency regulation technologies of variable speed wind turbine generators（WTG） were then introduced with the development trends analyzed, including inertia control, over-speed control, pitch control, and their combinations, as well the participating of energy storage system. This paper was concluded with some key issues to be researched in the future.