Abstract: In a process of load shedding of pumped storage units, the pressure fluctuation caused by the closure of the guide vanes seriously affects the safe and stable operation of the unit and pipeline system.As important factors affecting the dynamic characteristics of units, the layout of the pipeline structure and the initial working condition have an unclear influence on the head and speed of the unit during the load shedding process.In order to solve above problems, a refined mathematical model of the regulation system of a two-unit pumped storage unit was established based on the eigenline method and the improved Suter transform.By studying the internal relationship between the initial load, the pipeline structure and the maximum head and maximum speed of the unit, it is suggested that the unit connected by the branch pipe with small initial load and small water flow inertia time constant (T_w) preferentially shed load, which is conducive to improving the load shedding characteristics.Finally, the third-generation Non-Dominance Sorting Genetic Algorithm (NSGA-Ⅲ) and the Distance Evaluation Method for Superior and Inferior Solutions (TOPSIS) were used to construct an optimization model for the closing law of the guide vane, and by taking the maximum head and maximum speed of the unit as the objective function, an optimal closing law of the guide vane suitable for complex working conditions was obtained according to evaluation scores.The results of this study can provide theoretical guidance for the selection of the optimal guide vane closure strategy for pumped storage power stations under a layout of complex water transmission system.