Selenium (Se) is an essential element in the human body. The study aims to select selenium rich areas to delineate natural selenium rich land, promote the development and utilization of selenium rich land resources, accelerate the development of agricultural economy, and support rural revitalization strategies. This article takes Wulong Mountain, Longshan County, Hunan Province as the research area. Based on 1:50000 land quality geochemical survey data, a comprehensive evaluation is conducted around four aspects: soil selenium enrichment, environmental quality, irrigation water quality, and crop selenium content. A natural and pollution-free selenium rich land area is delineated, and the causes of soil selenium in this area are analyzed to explore its sources and influencing factors. The results show that: (1) The soil Se content in the study area is 0.19-0.84 mg/kg, with an average value of 0.48mg/kg, which is 2.24 times higher than the national surface soil. This indicates that the Se content in the soil of the study area is relatively high. The soil area with Se content greater than 0.4mg/kg is 15.18km2 (22770 acres), which has high prospects for selenium rich development. (2) The environmental quality of As, Hg, Cr, and Pb elements in the research area is lower than the screening value of the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard", and the environmental quality index of Cd element is lower than the control value. The soil environmental quality is excellent, the irrigation water quality is good, and the selenium rich rate of crops is 80%. (3) There is a significant positive correlation between Se and Cd, Cu, Hg, Ni, Pb, Zn, P, N, and organic carbon in the soil of the study area, while there is a negative correlation with pH. The Se content in the vertical direction of the soil is mainly influenced by soil organic matter and clay minerals, exhibiting surface aggregation characteristics.In this study, a total of 13251 acres of natural and pollution-free selenium rich land were designated. Through analysis of the causes of Se, it was found that the natural selenium rich soil in the study area has a stable source of Se, providing a theoretical basis for local planting of selenium rich agricultural products, development of selenium rich industries, and support for rural revitalization.