The passivation behavior of phosphorous materials on soil Pb was studied based on isotope labeling method coupled with Tessier sequential extraction procedure.The results showed that most of soil Pb in different fractions could be spiked with the adding enriched 206Pb isotopes except for the residue Pb.After adding the phosphorous materials including shell powder，(NH4)2HPO4，hydroxyapatite and composite agents，the soil pH，soil organic matter contents and the cation exchange capacities were significantly(P<0.05)increased except for the hydroxyapatite with a slight increase of pH.In addition，the active Pb in the soil including water soluble fraction，exchangeable fraction，carbonate bound fraction and Fe/Mn oxide fraction could be significantly passivated(P<0.05)based on the measurement of 206Pb signals，except for(NH4)2HPO4 with a slight increase of water soluble Pb content.Especially，93.3% and 89.7% of Pb in the pools of exchangeable fraction in the soil were passivated by the composite agents and(NH4)2HPO4，respectively.The results also showed that the phosphorous materials significantly increased the inertial Pb contents in soil organic matter fraction and residual fraction.The Visual MINTEQ model was also employed to show the possible passivation mechanism，and the result showed that the composite agents and(NH₃)2HPO4 significantly reduced the activity of Pb2+ in the soil by forming four species of Pb phosphates including chlorophosphate[Pb5(PO4)3Cl].