In this paper, we discussed a method to identify the background content and polluted content of soil Pb in Daxing, Hefei on the base of Hazen probability curve. The background content of soil Pb is 27.2 μg/g, similar to the mean content of soil Pb in whole Anhui province (26 μg/g). We also obtained the threshold value of soil Pb between the background content and polluted content in the studied area, i.e., 36.3 μg/g, which is in accord with the meaning of Index of Geoaccumulation calculated from this threshold value of soil Pb. It proved that our method is feasible for other regions and heavy metal elements.