A uniform lighting design method based on a double free-curved surface is proposed herein. According to the theory of geometrical optics and energy mapping relationship, a double free-form surface lens is designed with a distance-to-height ratio of one. By discretizing the extended light source and lens surface, a new double free-form surface lens profile is constructed by inverse tracing the extended light source. The optical properties are simulated by using optical simulation software. The results have shown that uniform circular illumination distribution with a radius of 1000 mm is achieved on the target surface 1000 mm away from the extended light source, and the illumination uniformity is 92.3%. This method can effectively improve the illumination uniformity of the target surface based on an extended light source, and the design process of the free-form surface does not depend on feedback optimization. Accordingly, the design time is reduced and the process becomes simple and convenient.