The invention discloses a method for determining capacity of a pumped storage power station. The method comprises the following steps: calculating load prediction data in preset time according to historical load data, calculating the wind-electricity power prediction data according to historical wind-electricity power data, and calculating call wire power prediction data according to historical call wire power data; determining the boundary conditions; calculating the equivalent load prediction data on the day according to the load prediction data on the hth day in the preset time, the wind-electricity power prediction data and the call wire power prediction data; determining the maximum technical output requirements on the day in the conventional unit; determining the start-up mode on the day in the conventional unit according to the maximum technical output requirements on the day and the unit operation constraints; determining the minimum technical output on the day in the conventional unit according to the start-up mode on the day, and determining the wind curtailment electric quantity at each point on the day according to the minimum technical output on the day and the equivalent load prediction data on the day; and repeating the previous steps, acquiring the wind curtailment electric quantity data on each day throughout the year, and determining the capacity of a pumped storage power station according to the wind curtailment electric quantity data.