In order to solve the difficult problems of collimation, irradiance uniformity and spectral matching of existing LED solar simulators, a simple, efficient and high-power optical system design method of LED solar simulator was proposed based on photoelectric integrated secondary optical design. The small angle collimating lens and the parabolic mirror were utilized to integrate the light source, and the mixing light rod and microstructure were used to homogenize the light, finally the collimating output of light was realized by the parabolic mirror. Based on the design idea of coaxial collimation, the design of the LED solar simulator was completed.In addition, the optical software LightTools was used to simulate and optimize the optical system of LED solar simulator. The experimental results show that the irradiation inhomogeneity is 2.5% and the collimation angle is 1.5° on the effective irradiation surface with a diameter of 260 mm.