The traditional plant lighting design only optimizes the uniformity of a certain reference surface, which leads to the unevenness of the light environment in the plant growth space. In order to solve this problem, we conduct the research based on the spatial illunimation uniformity evaluation system. First, three potential design schemes are proposed for the stereo plant light sources with high spatial illumination uniformity, and the effect of structural parameters on illumination is studied with the help of the TracePro commercial simulation software. Further, the Taguchi method is used to optimize the experimental process and the optimal structural parameters are obtained with the ANOVA analysis. Then, the illumination effect during plant growth is tested based on the obtained optimal solution. Finally, the technical advantages of the stereo light source system compared with the traditional array LED light source are introduced. The experimental results show that the optimal structure can provide a uniform illumination space with illumination uniformity of horizontal planes and illumination uniformity of vertical planes of 92.00% and 83.12%, respectively, and with the red and blue color-mixed uniformity of two spatial reference planes of 94.19% and 90.70%, respectively. The plant light source system can meet the need of a uniform spatial illumination environment during plant growth.