An edge-lighting natural light flat panel light without light guide plate was designed. The collector collects the nature-light, then the light is transported to the panel lights with the help of PMMA optical fiber. In order to obtain uniform illumination, the beam from the fiber was converged by using a cylindrical lens and grazed through the reflective back panel with freeform surface. Furthermore, the effect of the flat panel light was simulated by using the Tracepro software. And different illumination maps for different angles which between optical fiber and the reflective back panel were get after further simulation. The simulation shows that the uniformity of illumination can reach 94.1% after optimizing the parameters of the flat panel light. This light not only can solve the danger of LED blue light, but also simpler the production process, which has a good reference for converting sunlight into the green lighting and functional lighting.