The present invention provides a method for optimizing the power capacity ratio. The method comprises the step of optimizing various power capacity ratios in a power grid system based on operating characteristics and constraints of various types of power sources and heat sources in the power grid system and aiming at minimizing the total fossil energy consumption of the system. The method provides a tool for analyzing the correlation between the conventional power source and the renewable energy source in the high-proportion renewable energy system, and better plans and guides the development and matching of the power source.