Abstract:A spectral model for cloudless and cloudy days to generate direct-norm al and diffuse horizontal irradiance in China is presented. In the model,the att enuation of various atmospheric constituents in different bands is calculated ,such as absorpti on of water vapour and uniformly mixed gases in the infrared spec tral region,ozone absorption, Rayleigh scattering and aerosol at tenuation in the ultraviolet and visible bands. The distribution of calculated results is given ,and the main factors that infl u ence solar radiation are discussed .The model is proved to be very accurate and applicable to a broad range of atmospheric conditions.