In general, the quantitative electron probe microanalysis is based on comparisons with standard samples. In this article, a method of the quantitative analysis of binary alloys without reference to standard samples is introduced. After simultaneous measurements of the ratios of the Ka photons of two elements in the binary alloys (Cu-Ga, GaAs) in SEM-EDS equipment, the constituents of the binary alloys are calculated from a simplified formula for the energy loss of the incident electrons, the X-ray excitation cross-section and the secondary fluorescence. When the overvol-tage of the incident electrons is kept in the range 2-3, the calculated results show good agreement with the actual constituents. The "instrument sensitivity" of the characteristic X-ray of the pure elements determined in the literature is calculated and discussed by using this simplified model.