Abstract: The multistage hydropower station with regulating reservoir is a main layout scheme to deal with the complex terrain problems in the development of southwest hydropower base. How to realize the flow matching of series hydropower station under load regulation conditions is the key to ensuring the safe and stable operation of units. For this purpose, from the perspective of hydropower station transition process and control, this paper establishes a two-stage series hydropower station transition process simulation model with regulating reservoir, and analyzes the dynamic variation of unit parameters such as unit speed, output and draft tube inlet pressure, as well as hydraulic parameters of regulating reservoir such as water level and flow under load changes. The results show that the regulation reservoir has no effect on the regulation quality of hydropower stations at all levels when the series power stations participate in the power grid regulation. However, if there is no follow-up regulation, the series hydropower station can only maintain the operation for a short time. Under the load redistribution condition after load rejection of some units, the inlet pressure of the draft tube of load distribution units decreases obviously. The adjustment time of load distribution unit and load distribution scheme also have no significant impact on the operation of series hydropower stations. The above research provides some technical support for the safe operation of the two-stage hydropower station.