The accuracy of a theoretical power calculation result for a photovoltaic power station affects the statistics of the curtailment electricity directly, and has a significant impact on power grid dispatching and photovoltaic development planning. The traditional calculation methods for generation power include the template inverter and meteorological data extrapolation methods. When the output of the template inverter is restricted, the template inverter method is inaccurate, and the parameters of the meteorological extrapolation method are numerous and difficult to determine. To solve the above problems, an optimization calculation method is proposed. First, the calculation principles of the template inverter and the meteorological data extrapolation methods are introduced, and the characteristics and shortcomings of the two methods are analyzed. Then, improved template inverter and improved meteorological data extrapolation methods are proposed based on the historical output of a photovoltaic power station and the meteorological information. In practical application, when there is no photovoltaic curtailment or the photovoltaic curtailment is in the initial stage, the improved template inverter method with higher calculation accuracy is used for calculation; when the output of the template inverter is restricted, the improved meteorological data extrapolation method is used. Finally, the simulation results for a domestic photovoltaic power station in different meteorological conditions verify the rationality and effectiveness of the proposed method.