Abstract: With the large-scale centralized development of hydropower, the large-capacity power grid with high proportion of hydropower has a certain scale, and its frequency safety problem is more and more prominent. The existing discrete control strategy is difficult to meet the control demand in the control accuracy. A precise control strategy for frequency emergency control is proposed for hydropower units. When there is a large power surplus in the power grid with a fault, the coordinated control strategy of traditional discrete generator shedding and rapid output regulation of hydropower units is used to realize the precise control of hydropower group in the case of fault. This paper puts forward a fast regulation method for the output of hydropower units. Through the security and stability control system, the rapid adjustment command of the output of hydropower units is directly issued to the speed regulation system of hydropower units, which can quickly adjust the output of hydropower units instead of some discrete generator tripping. It can effectively solve the over control/under control problems in the existing security and stability control system. The simulation results show that the proposed control strategy is feasible and effective.