By the example of designing freeform lens based on LED light source to achieve uniform circular spot, a new method of establishing optical device model is proposed. According to geometrical optics and non-imaging optics theory, the mathematical model of lens is derived. Numerical calculation of lens surface data is obtained by Matlab, and by TracePro programming the lens modeling is completed, then a conversation between Matlab and TracePro is created with the dynamic data exchange (DDE) protocol. In TracePro, the lens model is automatically created. The ray-tracing simulation results reveal that, the circular spot with the radius of 3 m on the target placed 5 m away is achieved by a LED Lambertian light source which has the luminous flux of 100 lm, size of 1 mm×1 mm and a viewing angle of 120°. The uniformity of illumination reaches 0.7, and the lens efficiency can reach 87%. This method can simplify the design process and save time compared with conventional methods of lens entity model, which further proves its accuracy and reliability.