Abstract: The characteristics of the light emitting diode （LED）limit its applications in various lighting fields. The allocation of LED power to form an ideal luminance on a target plane was investigated. This paper analyzed the designs of optical systems on different applications, obtained the formula of the lens by adopting etendue conservation method in non-imaging optics, achieved round uniform illumination with 85% uniformity and rectangular uniform illumination with 75% uniformity, established the 3D model of the freeform lens, and conducted the ray tracing based on TracePro. The simulation results meet the corresponding standard, which validates the design.