A cumulative feedback optimization algorithm based on illumination deviation restrained by energy mapping relationship and easy processability is proposed, and a freeform surface lens with uniform illumination distribution and light emitting diode (LED) of chip on board (COB) as light source is designed. In this approach, the new target light distribution is modified by accumulating the illumination deviation after each iterative feedback optimization between the simulation light distribution and the target light distribution to the presupposed target light distribution. The target light distribution after modification is then used to reconstruct the model of the freeform lens by combining the energy mapping relationship. Meanwhile, to make the designed lens easier to be molded and processed, the structure of the lens is modified by restraining concave plane of the lower half of lens into vertical plane in the feedback optimization progress. With this method, the corresponding freeform lens is designed with Cree CXA1816 COB LED as light source. The results show that the uniform illumination distribution in a circular region with a distance of 1000 mm from light source and a radius of 1480 mm can be achieved after 3 times feedback optimization. Finally, according to the design results, the corresponding lens is fabricated, and the illumination effect is tested. Actual measured illumination of the lens is consistent with the simulation results.