Abstract: In dissolution of sample,silicon was expelled as SiF4 by evaporation with HF and HClO4,while phosphorus was oxidized to PO3-4 simultaneously in fuming with HClO4.An aliquot of the sample solution was taken and the orthophosphate in the solution was separated from the matrix Fe(Ⅲ) and other co-existing cations by cation exchange.Eluates from the ion-exchange column were collected in a volumetric flask and the PO3-4 in the solution was precipitated as lead phosphate by reacting with an excess amount of lead standard solution.Content of phosphorus was found indirectly by FAAS determination of excess amount of Pb2+ ion in the filtrate.Linear relationship between values of absorbance and concentration of phosphorus was found in the range within 2.0 mg·L-1,with a detection limit of 5.9 μg·L-1.The proposed method was applied to the determination of 3 standard samples,giving results in consistency with the certified values,and values of RSD′s (n=11) in the range of 1.7%-4.0%.