Selenium is a trace element that is necessary in the human body. Selenium has an immune boosting effect, so in the current research it is believed that selenium deficiency may have some relationship with the appearance of cancer. Selenium is more common in daily life and is mostly contained in food, so as long as the diversification of food is carried out, selenium can meet the body’s needs normally. Selenium has a high status among the trace elements in the human body, mainly because it can prevent and fight cancer, and it can assist in the identification and treatment of cell mutations in the human body. Selenium can scavenge free radicals, lower blood lipids, can delay aging, enhance disease resistance, and have a certain alleviating effect on the side effects of radiation and chemotherapy for tumor patients.