A design of the freeform lens made by PMMA for the LED flat light applications was presented. This lens can be used to achieve the uniform illumination of the flat target of the LED flat light, which is based on the principle of freeform surface of the refraction and total reflection principle which realize redistributing the out light. A numerical method and experimental method were used in the design. The simulation results show that when the distance between the freeform lens and the flat target is 5 mm, rotation angle is 0°, the distance of the freeform lens and the LED is 7 mm, the uniformity of the whole lamp is up to 96.6% with the high luminous efficiency. The experimental results show that under the action of freeform lens, the uniformity of the flat target of the LED flat light without the guide plate is 95.74%, which is similarly equal to the digital simulation.