Ultraviolet (UV) spectrum is an important method for photoelectric measurement. Ultraviolet target signal is weak, only a few kinds of optical materials in this spectral range can be chosen, so it′s difficult for the high-resolution ultraviolet observations. A large relative aperture and long-focus UV optical system is designed which is used in target range measurement, and it solves those problems by catadioptric imaging and reimaging. The UV optical system has the parameters of F number of 2, focal length of 400 mm, field of view (FOV) of 1°, wavelength range of 250~400 nm. The Nyquist frequency (38 lp/mm) modulation transfer function (MTF) is better than 0.7 in the telescope system FOV according to the analysis of optical software. Taking into account the environmental adaptability, focusing amount and image quality are considered at -40 ℃~60 ℃ for the UV telescope system. Result shows that the Nyquist frequency MTF is better than 0.5 after focusing which meets the design specifications and the practical application.