Abstract: Dry ashing with auxiliary method and on-line internal standard with direct introduction of organic solvent method are established to determine the P content in biological oil with inductively coupled plasma optical emission spectrometry (ICP-OES). The multicomponent spectral fitting model of phosphorus was used to eliminate the spectral interference of copper. In dry ashing method, the kinds and addition amount of auxiliary were investigated and the organic magnesium was finally selected as the best one. The recovery of phosphorus from 1,2- dioleoyl-sn-glycero-3-phosphocholine is 104%±1%. The limits of detection of two methods were 0.013 ?g/g and 0.264 ?g/g, respectively. Besides, the article points out the shortage of density correction in the ASTM D7111-05 and redressed.