Ultraviolet (UV) detection principle and configuration of UV detection system are introduced. The experimental system is designed and established. The system wording at 240～280 nm achieves the focal length of 200 mm and F number of 6. The UV image is converted to visible image at the CCD through the relay system. The estimation method and model are proposed according to the formula of image plane irradiance and imaging， which are based on the UV radiation performance of typical targets and atmospheric transmission performance of UV radiation, combined with the performance parameters of UV warning system. The detection distance of UV warning system for a typical target at different angles is computed and validated. The analysis and conclusion show that the detection distance of UV warning system can increase by changing the performance parameters of detector, such as CCD minimum illuminance, image intensifier′s gain , optical system′s transmittance and relative aperture.