Selenium deficiency is an important factor leading to gastric diseases such as gastric ulcer disease. The decrease of selenium level in human body will cause the lack of immune function and the decrease of antioxidant capacity, which will cause the instability of gastric mucosal barrier and the xanthine oxidase will continue to rise in emergency situations, causing ischemic damage to gastric mucosa and the increase of oxygen free radicals, leading to gastritis, gastric ulcer and other digestive system pathologies. Selenium is a natural antioxidant, and selenium supplementation can rapidly improve the activity of selenium-containing enzymes in human body, which can effectively inhibit the generation of reactive oxygen species, enhance the antioxidant function of the body, scavenge the free radicals generated during human metabolism, stop the necrosis of gastric mucosa, promote the repair of mucosa and healing of ulcers, and prevent cancer. The selenium and zinc in the serum of patients with various acute and chronic gastric inflammatory diseases are significantly lower than those of healthy people, while those of patients with gastric cancer are even lower. Five percent of patients with chronic gastric diseases may become malignant. Selenium is one of the 15 essential trace elements in human body, which has a strong antioxidant effect of scavenging “free radicals”; selenium has the function of regulating immunity and repairing damaged cells, and has a protective and repairing effect on damaged cardiac muscle cells, liver cells and gastric mucosa cells. The appropriate amount of selenium supplementation can effectively improve the body’s immunity and resistance to disease. For patients with chronic gastric disease who do not need surgery for the time being, through trace element supplementation and dietary regulation, it can promote the healing of digestive tract mucosal lesions. Therefore, reasonable selenium supplementation is necessary.