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In order to obtain reliable radiation for design, operation and economic assessment of solar energy conversion device, a statistical analysis of daily correlations between diffuse solar radiation and global solar radiation is carried out using 10yr data (1995-2004) of daily global and diffuse solar radiation obtained at Beijing meteorological station of China. The accuracy of the correlations is performed in terms of the coefficient of determination, R2. The results indicate that the correlations relating the diffuse fraction (Kd) with the clearness index (Kt) are reliable for diffuse radiation prediction at Beijing, China. And the quadratic model of the whole period is preferred for both its accuracy and its simplicity.