Abstract:  The study estimated the solar ultraviolet (UV) irradiance at noon for clear sky based on the physical mechanism of atmospheric radiation transmission. Then UV irradiance of clear sky was corrected revised using factors such as cloudiness, aerosol and etc.. Finally, daily maximum UV irradiance under of non-clear all-sky conditions was obtained and UV intensity forecasting model was constructed. Compared with the original national UV intensity grade forecasting model, forecasting accuracy of the new model is greatly improved, which makes the new model can be applied to the national operation of UV intensity forecasting. The results indicate the improved model works better under for clear- sky than under for cloudy- sky.