Abstract: Selenium (molecular weight 78.96), is a necessary non-metallic trace elements. In recent years, more and more studies have found that selenium is closely related to human disease and could not be ignored. In this paper, we elucidate the in vivo absorption and metabolism of selenium; the active substance-selenoprotein P and so on; the correlation between selenium and pathogenesis of various diseases such as cardiovascular disease, AD/PD neurodegenerative diseases and cancer, etc. The aim is to achieve a more comprehensive understanding of selenium, and to research the in vivo process and the biological effects of selenium. At the same time, selenoproteins and related mechanisms might also be a new target for drug research and discovery.