In order to improve the light efficiency and illumination uniformity and reduce glare, LED street light need secondary light distribution design. Based on the basis of space Snell law, combing with bidirectional iteration algorithm and equivalent grid dividing, this paper realizes one-to-one correspondence between LED emergent ray space and specific spot on the road. A freeform surface lens was generated, and it can convert light distribution of the LED to rectangle. Simulation results show that LED′s light energy is almost limited in a rectangular area of 30 m×13 m, the whole light efficiency is 90.4%. The horizontal illumination uniformity and vertical illumination uniformity can reach 83.2% and 71.7% respectively. When multiple LEDs are arranged in 30 m spacing, the facula width on the pavement is about 14m. At this time, vertical illumination uniformity increased to 77.2%. Experiment results show that the light distribution curve of LED street light is bat-wing distribution. The horizontal and vertical average illumination is 31.17 lx and 25.72 lx, and energy is limited in ±62° and ±40°, respectively. It can meet requirements of national standard for lighting design of urban road, which prove the feasibility and practicability of the lens design algorithm.