Aiming at lower irradiation uniformity of the traditional solar simulator, an optical integrator is designed which can effectively improve the irradiation uniformity of sun simulator. The composition and working principle of optical integrator is introduced, optical optimization design technology of optical integrator is described, optical and mechanical structure of the optical integrator is designed reasonably, and the ansys software is used for thermal analysis of the machine structure. Finally, lightTools software is used to be simulating for solar simulator. The results show that: after using the optical integrator, irradiation non uniformity of the sun simulator is markedly improved, irradiation non uniformity in 60 mm range is less than ±1%, and in (60~200) mm is less than ±2%, instability is better than ±1%/h, which agree with the test data and can meet the requirements of high-precision.