Based on the data of direct clear-sky radiation from 68 observing stations in China,a discussion is made in detail of the computation methods for atmospheric transparency coefficients P₂,P_d and P_w,whereupon a new and more reasonable method for calculating the components P_L,P_d and P_w is Suggested. The main factors affecting atmospheric transparency are analyzed and the spatial distribution of P₂,P_d and P_w is plotted. A discussion of the modes of distribution leads to some interesting results.