Abstract: Abstract:  The distribution of selenium in soil is uneven, and its distribution and origin is not clear. In order to study the spatial distribution and causes of high-selenium soil in Langao County, the Se-rich core area of Ankang, Shaanxi Province, 767 surface soils samples were collected from the whole county. In the typical high-selenium areas (Zuolong Town and Minzhu Town), the plots of administrative villages (most of the cultivated land in the mountainous area is very small, no more than 1 mu) were taken as units. A total of 409 soils, 18 potatoes, 35 corns and 14 bedrocks were collected by encryption. The contents of total selenium, total arsenic and other trace elements were measured by HG-AFS and ICP-MS, respectively. The results showed that the average soil selenium content of Zuolong and Minzhu Towns in northern Langao County was 3.38 mg/kg (0.02-37.39 mg/kg) and 3.11 mg/kg (0.05~16.96 mg/kg), respectively, which were far higher than the background values of soil selenium content in China and the world. The selenium content above 0.4mg/kg in the surface soil of Zuolong Town and Minzhu Town accounted for 99.18% and 75.79% of the respective township area, respectively. The selenium enrichment rates of potatoes (0.04~1.78 mg/kg, mean 0.49mg/kg) and corns (0.01~2.82 mg/kg, mean 0.69mg/kg) in the high selenium zone were both over 68%, but there were potential health risks. The main reason for the enrichment of selenium in the soil in the high selenium area is that the selenium-enriched strata in the Late Precambrian-Cambrian was exposed in a large area, resulting in a correspondingly higher selenium content in the overlying soil formed by weathering. Therefore, these two towns are veritable selenium-rich areas.