Abstract: Optical lenses are the most basic components in optical instruments; focal length of the optical lens is the most important characteristic parameter, and accurate measurement of the focal length of the optical lens has long been a research focus. However, few studies have been conducted on the UV lens focal length measurement. In this study, a method for measuring the focal length of an ultraviolet lens based on a reflective collimator is investigated, according to the characteristics of the ultraviolet lens, and a few UV lens focal length measurement systems were designed. Different UV lenses were studied, and the focal length of the system was chosen for the measurement error analysis. The experimental results show that the measurement system can measure the focal length of the UV lens with high precision, i.e., the measurement error of 25-mm lens is 2.041%, that of 100-mm lens is 0.934%, which verifies the accuracy of the measuring system.