Abstract: It is discovered that relation of square power function exists between mass attenuation coefficients and mass coherent scattering coefficients of elements of atomic number 6-40 to 20 keV X-ray. Accordingly, a new prinople of square power method of RhKα coherent scattering for quantitative X-ray fluorescence analysis is suggested. This principle has been proved to be correct and superior to traditional scattering technique with geochmical reference GBW as internal standard. This method has ben applied to determine microelements in geochemical samples.