Taking the cultivated soil layer in the Wuying Township - Sanhe Town area of Suihua City, a typical core distribution area of black soil in China, as the research object, this study investigated the content, distribution and occurrence forms of selenium in the soil by using geostatistical analysis and other methods, and explored the influencing factors of soil selenium availability. The results showed that the distribution of selenium in the surface soil of the study area was relatively uniform, with an average content of 0.343 mg/kg, which was higher than the national average. About 15% of the plots met the standard of green selenium-rich land. The contents of various forms of selenium in the soil from low to high were ion-exchangeable, iron-manganese bound, water-soluble, carbonate-bound, residual, humic acid-bound and strongly organic-bound. The water-soluble and ion-exchangeable selenium, which are easily absorbed and utilized by plants, accounted for only 2.5%, while the iron-manganese bound, strongly organic-bound and residual selenium, which are difficult to utilize, accounted for 58.4%. The available selenium content in the soil was 0.007-0.02 mg/kg, and the selenium activation rate was 2.06%-6.19%. The available selenium contents and selenium activation rates in paddy fields were higher than those in dry fields. The occurrence forms of selenium in the soil and soil physical and chemical properties affected the availability of selenium. The available selenium content in the soil was positively correlated with the total selenium, nitrogen, sulfur and organic matter to varying degrees, and negatively correlated with manganese, magnesium oxide, silicon dioxide and pH to varying degrees, indicating that high organic matter and nitrogen and sulfur contents in the soil were conducive to the activation and release of selenium in the soil.