Abstract: To analyze samples without using standard, the energy dispersive X-ray fluorescence analysis (EDXRFA) of unknown samples was studied. The ratio R of coherent and incoherent scattering peaks of K_α in the original spectrum of target Rh was got through the measurement of Ti, Fe, Ni, Cu, Zn, Sr, Sn, Pb single element standard samples, then the relationship between R and the effective atomic number of the corresponding single element standard samples was established, and the fitting curve of Z_eff-R was obtained. When it comes to solve the unknown samples, measure the unknown samples and get the R, then the effective atomic number of the unknown samples was obtained by substituting the R of unknown samples into the Z_eff-R fitting curve, and then the atomic number could be used in the fundamental parameters method iteration to calculate its mass attenuation coefficient. The Ti, Fe, Ni, Cu, Zn, Sr, Sn, Pb single element standard samples were again used to calibrate the instrument and obtain G_i parameter which was applied in the fundamental parameters method iteration of the corresponding element when it comes to solve the unknown samples. In order to verify the reliability of the algorithm, the 15 national soil standard samples were analyzed through the algorithm of this article. The results showed that the calculated content of Ti, Fe, Ni, Cu, Zn were close to the standard content, and some low content element’s content errors were a little larger because of the scattering background and other factors. The results showed that this algorithm could be used in the situ energy dispersive X-ray fluorescence analysis.