An optical design of double freeform surface semiconductor light-emitting diode (LED) collimating lens is proposed based on relevant theories such as geometrical optics, law of energy conservation, and the Fresnel′s law. Detailed algorithm design for constructing collimating lens model is presented as well. A freeform surface is a surface that is rotationally symmetric around a central axis. The 2D contour of this surface is constructed on the basis of non-uniform rational B-splines (NURBS) method and by ProE software. Through Monte Carlo ray tracing simulation, it is found that, compared with conventional single freeform surface collimating lens, double freeform surface collimating lens has greatly enhanced the illumination uniformity as well as the energy utilization. The research results have shown that, by using double freeform surface design, the design space can be remarkably extended, and the optical performance of collimating lens can be improved.