Abstract: Selenium is an essential trace element of human body, which encodes and synthesizes selenoprotein in the form of selenocysteine. Selenium and selenoprotein have a wide range of physiological functions such as antioxidation and immune regulation. Selenium deficiency is related to more than 40 human diseases such as cardiovascular and cerebrovascular diseases, cancer, diabetes, nervous system diseases, autoimmune diseases and infectious diseases. Selenium nutritional status is closely related to viral diseases. Selenium deficiency leads to the imbalance of redox and immune regulation, promoting virus infection and replication. Oxidative stress caused by selenium deficiency increases mutation rate of virus genome. A large amount of selenium is consumed by the host of infected virus to initiate antioxidant and immune response. The virus itself expresses selenoprotein to compete with the host with viral infection, while inhibiting virus replication by negative feedback regulation. The safe dose and toxicity of different selenium compounds used as therapeutic drug should be considered comprehensively. Recent studies suggest that selenium status is related to infection and pathogenicity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and more clinical and basic research is needed to explore the effect of selenium on viral infection diseases including coronavirus disease-2019 (COVID-19) in the future.