In order to solve the practical problems about the characteristics instability or loss to the optical system of the large solar simulator because of the overheating source, the radiator of the large solar simulator is studied. Through heat conduction analysis and the establishment of three-dimensional model, we established the radiator mathematical optimization model in working large solar simulator. Multi-objective parameters consisting of heat dissipating capacity, structure and solid mass of radiator were optimized based on the finite element analysis and the optimize regional value setting, and the final results of optimization show that heat dissipating capacity is not less than 11000 W when radiator mass is not greater than 16 kg. This scheme provides an effective design method for the optical equipment with the large size and the high working temperature.