The working principle of light guide and the light guide network design theory have been discussed. The formula for the distribution of non-uniform network is derived by using reflection, refraction, scattering theory of geometrical optics, and a large-size bilateral-edge LED backing guide plate is designed. The light guide plate model is debuged and simulated by using optical simulation software. And taking full account of the cost and feasibility, the result of uniformity is very close to 80%, which fully meets the need of advertising light boxes.