With the dual-carbon target, renewable energy power generation has been developed rapidly in China, in order to improve renewable energy consumption and renewable energy power plant economic operation, this paper presents an economic dispatch method for wind-solar-thermal combined power system considering green certificate trading and peak shaving service, and through the solar thermal power plant with heat storage to provide part of the peak load capacity, improve the operation economy. In this paper, firstly, the peaking mechanism of photothermal power plant and the green certificate trading are analyzed, and the frame of wind-solar-photothermal combined power generation system is put forward, in order to optimize the total cost of wind-solar-thermal power generation system, the optimal dispatching model of power system considering green certificate trading and peak shaving service is established, the effect of different capacity of heat storage system on the economy of combined system is analyzed by IEEE simulation example system, and the effectiveness of the proposed method is verified by comparison and analysis of three scenes.