According to the diurnal variation of color temperature and brightness of sunlight, a strategy was proposed to simulate the diurnal variation of color temperature and brightness of sunlight by light mixing of RGBW-LEDs, and the genetic algorithm was used to optimize the color rendering index. The simulation was conducted by Matlab, and the simulation results were validated by the sunlight simulation system based on the Arduino open source platform. The experiment shows that using mixed light based on RGBW-LEDs can accurately simulate the change rule of sunlight′ color temperature and brightness, and make LED mixed light have the optimal color rendering property through the optimization of genetic algorithm, so that the correctness and effectiveness of the proposed strategy were verified. The sunlight simulation strategy can be applied to the field of solar simulation and engineering practice for special lighting fields, such as enclosed environment lighting and plant lighting and so on.