Abstract: The new power system, which primarily based on renewable energy, is encountering significant obstacles in ensuring power supply. Therefore, it is important to fully utilize the abundant hydropower resources in southwest China to guarantee power supply during peak hours. However, due to the intricate operational demands of hydropower, effectively analyzing and quantifying the peak capacity and optimal scheduling of large-scale hydropower systems remains a challenge. This paper proposes a method for quantitatively characterizing the multidimensional analysis of hydropower peak capacity, consisting of peak capacity, peak energy, and peak duration, based on analyzing key operational boundaries of large-scale hydropower from an engineering practicality perspective. Considering the complex operational constraints of cascade hydropower, a hybrid optimization approach for cascade peak capacity allocation is presented, combining the quantification of peak capacity, improved successive load shedding, and electricity-based water regulation. The case studies in the Jinsha River and Lancang River cascade hydropower systems in Yunnan demonstrate their effectiveness in characterizing the peak capacity of hydropower. Compared to other models for hydropower peak scheduling, the proposed method significantly improves computational efficiency, accuracy, and the smoothness of hydropower output while ensuring the same peak scheduling effect, which aligns more closely with the requirements of engineering practicality.