For the special use demands of ultraviolet warning cameras, the structures, distortion balances and the consistency of image plane illumination of ultra wide-angle optical systems were analyzed. An ultraviolet optical system with a large field of view of 120° and a large relative aperture of 1/2 was designed. The system is a double imaging configuration with the spectral range from 0.254 m to 0.272 m. By using inverse telephoto structure, its back working length is 7.48 mm. A quasi-telecentric optical system was selected to improve the illumination uniformity for off-axis and on-axis view fields. Then, by choosing optical materials and distributing the focal powers reasonably, the optical system was optimized. The experiments demonstrate that the system is characterized by smaller imaging distortion and uniform image plane illumination, the dispersion spot diameter is smaller than 63.5 m, and the relative distortion at 0.71 field of view, the relative illumination uniformity for off-axis and on-axis view fields are less than 20% and 10%,respectively. The structure of the whole system is compact and feasible, and is suitable for ultraviolet warning cameras.