In this study, 275 soils were sampled from Ximeng County to conduct a systematic analysis of the contents, spatial differentiation characteristics and influencing factors of soil total and available selenium (Se) contents with the methods of variance analysis, correlation analysis, geostatistical analysis, GIS spatial analysis technology and geographical detector. The results showed that the average contents of soil total and available Se were 0.49 mg/kg and 0.056 mg/kg, respectively, and the activation rate of soil Se was 12.17%. There was a significant positive correlation between soil total and available Se in spatial distribution, and the hot spots were mainly distributed in the eastern region of the county. Geodetector analysis showed that the rock type, elevation, and organic matter content have significant impacts on the spatial variation of soil Se elements. The spatial variations of total Se and available Se in the soil were not mutually exclusive for different factors. The interaction between factors collectively increases the impact on the spatial variation of total Se and available Se. In conclution, the soil in Ximeng County is rich in Se, and the spatial distribution of soil Se content is influenced by various factors such as geological conditions, resulting in significant areas of Se resource enrichment. The research results provided scientific basis for regional selection and planting management for the development of Se rich agricultural products in Ximeng County.