We propose an optimized uniform illumination design method for the ultraviolet (UV) light-emitting diode (LED) array module considering its application in UV light purification systems. First, the geometrical optics theory is used to evaluate the illumination of the purification layer receiving surface based on the luminescence intensity distribution in case of a single LED. Then, by combining the requirements of the spacing between the array module and purification layer, the ratio of the minimum and maximum illuminances of the purification layer, and illumination angle of a single LED, the optimal array spacing and simulation results of illuminance distributions are obtained by the dichotomy method along with the TracePro simulation. Finally, an uniform illumination measurement test has been designed for the array module to verify the accuracy of the simulation results. The research results demonstrate that the proposed method can realize an optimal design of the LED array module under different requirements with respect to the illumination uniformity, structure, and light source; furthermore, the proposed method exhibits important guiding significance for the design and development of UV light purification systems.