Abstract: Ultra-low frequency oscillations are apt to occur in a system with high proportion of hydropower formed on the hydropower DC island or asynchronous interconnection project, threatening the safe and stable operation of the power grid. Firstly, this paper studies the influence of the changes of hydropower ratios on the damping level in the system. Secondly, it analyzes the selection and sensitivity calculation methods of the strong negative damping units in a multi-machine primary frequency system. Finally, the optimization strategy of the multi-machine system governor is proposed. Combined with the transient frequency index, the balance between the stability and the speed of the primary frequency regulation in different hydropower proportional systems is realized, which provides a reference for engineering applications.