Abstract: In order to maximize the power generation of photovoltaic power generation system under the premise of ensuring the reliable operation of the system, a capacity ratio and variable power limit setting method based on the cost of photovoltaic power system is proposed. The influence of capacity ratio and variable power limit on the life of photovoltaic inverter and the power generation of the system is analyzed. The optimal setting model of capacity ratio and power limit parameters of photovoltaic power generation system considering the lifetime of power devices is established, and the optimal capacity ratio and power limit are obtained by using differential evolution algorithm to solve the model. The analysis results of examples in different latitudes verify the effectiveness of the proposed method.