Abstract: Installation of two upstream series surge chambers is a significant and feasible measure for peak pressure control. This paper presents a study on the stability of waterpower-speed control system for hydropower station with such a measure. For this system, we developed a complete mathematical model including diversion pipeline, surge chamber, hydraulic turbine, speed governor, and generators, and derived a comprehensive transfer function and linear homogeneous differential equation that describe the system's dynamic characteristics. The effects of fluid inertia in water diversion system and the surge chamber parameters on stability conditions are also analyzed in this paper using stability domains. The main conclusions are as follows. When the control system reaches the same stability domain as that with one upstream surge chamber, the total cross-sectional area of the two chambers is greater than that of one chamber. If the second chamber or the one closer to the plant is smaller, a greater total area is required to reach the same stability domain. The smaller the ratio of pipe flow water inertia between the two chambers over that between the pipe intake and second chamber, the smaller the difference between the total cross-sectional area of two chambers and that of one chamber system.