According to non-imaging optical principle, a method to obtain freeform based on longitude-latitude division and tangent-plane iteration was proposed. Firstly, a relative position model was constructed in three dimensional coordinate system, and the freeform was divided along its longitude and latitude direction with uniform angel. Secondly, because the energy of both each longitude and latitude freeform micro-belt and each corresponding micro-belt on the target plane was equal, the target plane was divided into grids and each coordinates of corresponding points on the target plane were obtained accurately. Finally, by choosing an initial grid node on the freeform, and using Snell equation and tangent-plane iterative method, the coordinates of all grid nodes on the freeform were obtained, which could be synthesized for the freeform surface. The simulation using the designed LED lens shows that for the axial symmetry target plane with uniform illumination, the corresponding optical system can be obtained quickly and accurately with this method, which enables LED light source to be applied in road lighting system.