At present, the large backlight modules, used in illuminating advertising pictures, are designed and developed in various specifications, whose common goal is to try to manufacture thinner backlight modules and produce more uniform illumination. The currently well developed backlighting technology for liquid crystal displays (LCDs) can be transformed and used in such an area. However, the design of edge-lit backlight with size of over 1 square meter has great difficulties in eliminating the phenomenon of non-uniform illumination. In this paper, the application of Bezier curve in the simulating the dot pattern on the bottom of light guide is presented, which directly determines the final light extraction efficiency and illuminating uniformity. Taking the RMS deviation of illuminance values at several sample positions as the merit function, the shape of Bezier curves can be smoothly changed, so that the dot radius can be optimized in a fast and efficient way. Such an optimization procedure uses only two variables and has a fast convergence. As an example, a large light guide, 800mm×1000mm in size, was designed by applying the Bezier method, and the final uniformity of 70% was achieved. The most prominent feature in such a method is that the thickness of designed light guide can decrease to 5 mm. In sum, the large sized edge-lit backlight can be designed in a short optimization period by simulating the dot radius distribution in a shape of the Bezier curve.