A telecentric ultraviolet warning optical system with a large relative aperture and a long focal length is designed using ZEMAX. This optical system contains six pieces of spherical lenses and has a total length of 154 mm. The system has a focal length of 100 mm, a relative aperture of 1∶2, and a field of view angle of 10°. CaF2 with a negative temperature coefficient of the refractive index is used as a concave lens for thermal compensation. The result shows that the average light modulation transfer function of each field of view is >0.4 at 10 lp/mm. Further, the biggest root-mean-square radius of the spot diagrams is smaller than 50 μm. With the advantages of excellent imaging quality, compact configuration, and wide temperature adaptability, the system is suitable for ultraviolet warning cameras.