Since the complementary benefit of a multi-energy complementary power generation system integrating new energies can hardly be quantified,a complementary benefit evaluation method for a wind-solar combined power generation system with a photothermal power station based on Monte Carlo and credible capacity is proposed. The method sets up the output model of the complementary system based on sequential Monte Carlo,realizing the probabilistic production simulations for the wind turbines,solar panels and photothermal units. According to the calculated credible capacity of the combined power generation system, the evaluation indicators for the system are obtained. By comparing the complementary benefits of a wind-solar-photothermal combined power generation system under different proportions of installed wind turbines and photothermal units, the complementary benefit evaluation for the system is completed. Finally, the evaluation method is verified by IEEE-RTS.The results show that this method can effectively evaluate the complementary benefit of the wind-solar combined power generation system with a photothermal power station.