For the LED extended light source, the bidirectional feedback mesh design method is used to design the freeform lens. Divide the energy grid of light source and target surface, and according to the feedback coefficient is established for each iteration curve, the mesh points are modified, and a new mapping relationship is established. Finally, two kinds of freeform lenses with no illumination in the center of the illumination area are designed. The Monte Carlo method is used to simulate led extended light sources with different sizes. The results show that for the LED extended light source with a size of less than 4mm×4mm, the uniformity and light energy utilization of the designed freeform lens in the lighting area can reach more than 90.5%, and it is suitable for road lighting occasions.