In order to solve the problem that the real solar angle and true irradiance (one solar constant) can not be simulated by the existing solar simulator at the same time, a new type of solar simulator optical system was designed. The design method of the optical system of the condenser was described, and the optimization technique of optical integrator and defocusing effect of projector lens were discussed. Using Zemax, optical integrator was designed by sequence and non-sequence, and the field diaphragm and the collimating lens system were also designed. The optical system was simulated with LightTools software, and the results show that 32′ of real solar angle and a constant solar irradiance can be achieved by the solar simulator, irradiation non uniformity in Φ100 mm range is less than ±1.6% and in Φ(100~300) mm is less than ±3.8%.