Abstract: According to the detailed soil geological survey data in the south of Fangshan, Beijing, it is found that the total amount of soil selenium is consistent with the available Selenium in spatial distribution through the cumulative frequency classification of soil available Selenium.Further correlation analysis showed that the content of elements C, N, S, organic matter and heavy metal elements Cd, Pb, Cu, Zn in surface soil had a high correlation with the content of selenium in soil, and a low correlation with the content of element P and pH value.Through the relevant study on selenium in six crops, cash crops and vegetables planted in the study area and selenium content in corresponding root soil, it is found that wheat and maize had the strongest Selenium enrichment ability and were the alternative varieties to enhance the added value of agricultural products.The vertical distribution characteristics of total selenium in soil profile show that selenium belongs to surface accumulate type, and with the distance from the mountain front, the proportion of effective selenium is higher and the proportion of difficult to migrate is lower; Finally, combined with the comprehensive demonstration of geology, geotectonics and petrochemistry, it is concluded that the selenium elements in the selenium rich soil in the study area are mainly from the coal measures strata of Yangjiatun, and the main ways are Zhoukoudian River and Mapuiquan River, supplemented by Dashihe River.