Based on geochemical study of soil, the high selenium soil in Beijing Plain was discovered distributing discontinuously around the west of plain and scatters in the city. The content of selenium in surface soil is from 0.04 to 5.26 mg/kg, with the average value of 0.20 mg/kg. The content of selenium in deep soil is from 0.043 to 0.22 mg/kg, with the average value of 0.081 mg/kg. The selenium tends to enrich in the surface soil. The content of selenium in shale is higher than that in other types of rocks. The source of selenium in soils is from the weathering of Se-rich carbonaceous rocks in the west part of Beijing. Studies show that the soil organic matter is closely related to selenium, and that organic matter plays a key role in adsorption and fixation of selenium in surface soil.