The present paper has revised and tested previous research results of theoretical analysis.Intensities of 18 characteristic peaks were picked up from 63 powder patterns of Ca-amphiboles which include 50 data from references and 13 measured data. By means of stepwise regression a series of experimental formulae were fitted between 18 characteristic reflection intensities and 11 cation site_occupanices to estimate the cation site_occupancy of Ca-amphibole with the precision of 78%~96%. As for Mg, Fe2+inΣsite (M1+M3+M2), K and vacancy Em in A site and Si in T1site, the cation site-occupancy precisions approach 90%. The precision is up to 80% for named crystal chemical class in amphibole nomenclature. It is evident that the calcula- tion of the cation site-occupancy of amphibloe group by X-ray powder diffraction is not only practical but also reliable. The authors have succeeded in extending this method to the alkali-amphibole subgroup. As Ca_Na ampohibloe subgroup is among 52 alkali_amphibloes, the method of estimating cation site-occupacies by X-ray powder diffraction is suitable for the whole amphibole subgroup.