Abstract: This study aims to determine the selenium (Se) background values of oils along the northern margin of the Qinghai-Tibet Plateau and serve the utilization of Se-rich resources, as well as the prevention and control of Se deficiency risks. To this end, this study systematically collected 8 273 surface soil samples and 2 190 deep soil samples, analyzed and tested the Se content and other relevant indicators, and examined the response relationships between soil Se and factors such as soil type and physicochemical properties. The results indicate that the surface and deep soils exhibit Se background values of 0.188×10^-6 and 0.153×10^-6, respectively. High Se background values are identified in the Menyuan Basin, the Xining Basin, the northern part of Qinghai Lake, and the Lagrange and Daban mountains. The highest Se background values occur in soils with the weathering materials of red and coal-bearing clastics of the Paleogene Xining Group as parent materials. The Se background values exhibit a negative correlation with pH and a positive correlation with the contents of organic matter and iron-aluminum oxides. Se in soils tends to accumulate in woodlands, grasslands, peat-rich marsh soils, and meadow soils. The study posits that the soil-forming parent materials with Se background values, including red and coal-bearing clastics of the Paleogene Xining Group, serve as the primary factor controlling the formation of Se-rich soils, and the secondary controlling factors include carbon-rich forests, grasslands, meadow soils, and marsh soils. The transportation by water streams and sedimentary transformation of these controlling factors contribute to the formation of the spatial distribution pattern of localized Se enrichment in the soils of the northern margin of the Qinghai-Tibet Plateau.