We present a resolution testing system of ultraviolet (UV) imager.In this system, an UV Czerny-Turner monochromator with a small f-number is designed to get more energy as an UV radiation source, and its stray light is rejected effectively by light traps.And UV diffuser is employed in order to get uniform light distribution on the resolving power test target.We also design a novel UV collimator which makes infinite UV testing targets.It can reduce the difficulty of optical design and the machining cost, and utilize UV energy at maximum extent.This facility has been applied in the imaging quality evaluation of the UV instrument, and the results accord with the theoretical analysis.