In order to resolve the problem of matrix correction in the determination of the trace elements (including rare earth elements) for rocks, this paper has made a study on the relative absorption including incident and fluorescence absorptions and its relation with the wavelength. A general equation of calcu- lation the cofficient of absorption correction is described, in the case that there is an absorption edge of the major elements between the analytical line and the coinpton peak of the characteristic target line. The problem of matrix correction in the determination of most elements of which the effectivety re- solved by this method.