Freeform lenses are playing a more and more important role in LED secondary optics design. In this paper, based on the lighting-energy conservation law, edge-ray principle and Snell's law, we present a freeform lens optical system design method for LED lighting. This system can achieve rectangular lighting area, and it is easier to precisely control the angle of light emitting and processing, with the advantages of uniform illumination. The software Matlab and Rhino were used to get the model of lens, and the PMMA was used as the material to design lens model. Finally, the numerical simulation results showed that the spot shape was close to the expected results.