A free-form secondary lens is proposed to optimize an LED light. Based on Snell's law, energy conservation law, and a Monte Carlo ray-tracing algorithm, the surface contour of the free-form lens can be determined according to the requirements of an LED light. Optical experimental results show that an optical efficiency of 95.69% can be achieved by the lens, of which the illumination uniformity 0.317 is higher than the commercial illumination uniformity 0.259. The lens does not need the help of a white ring holder, so the cost of the LED light can become effective.