Abstract: XRFS was applied to the determination of phosphorus in alloy. Mα line of tungsten and Lα line of molybdenum were used as reference lines for measuring the overlap interfering coefficient. Potassium and scandium which are not present in the alloy were selected as replacing elements of tungsten and molybdenum,and the actual 2θ angles measured were Mα of tungsten and Lα of molybdenum. Two sets of standard samples,one containing only molybdenum and the other containing both tungsten and molybdenum,were used to measure the overlap interfering coefficient and calibration curve was made to analyze phosphorus .The proposed method was applied to the analysis of standard samples,giving results in consistency with the certified values,and RSD (n=10) found was 0.68%.