Based on the diffuse solar radiation data of 64 solar radiation observatories from 1971 to 1985,the correlation coefficients between the total cloud cover, relative sunshine and the diffuse solar radiation are calculated. Then the experimental equation is established as the following:D=Q0(s1+0.01) (a+bN), where Q0 is the extraterrestrial radiation, s1 is the relative sunshine, N is the total cloud cover,a and b are experimental constants and Dn is the net diffuse solar radiation that is given by Dn=D/ (s1+0.01). The net diffuse solar radiation is the diffuse solar radiation of unit relative sunshine. With the experimental equation,diffuse solar radiations for more than 200 places where none of the solar radiation observation is calculated. Last,the distributions of monthly diffuse solar radiation in China is discussed.