Abstract: A design with two parallel fly-eye lens arrays was proposed, in order to achieve a uniform rectangular light spot of large area. TracePro simulation was used to analyze the impact of the parameters, such as the space between two fly-eye lens and the back working distance of the optical system, on the size and uniformity of the light spot. The simulations indicates that the smaller the distance between the two lens and the longer the working distance, the larger the formed spot size. The best uniformity of light spot is obtained when the space between the two fly-eye lens is close to the focal length of the first lens. In one design, a spot with size 350 mm200 mm was obtained on the target plane, which was 1m away from the light source. In the central region of the spot, a range of 280 mm160 mm, which covered more than 60% of the total area, produced a light illumination uniformity higher than 85%. This design is expected to be used in medical phototherapy, street lighting, and many other fields.