Oxygen therapy refers to the treatment of all kinds of hypoxia, except to eliminate the cause of hypoxia, oxygen therapy can be given. High concentration of oxygen inhaled to increase dissolved oxygen content in plasma can improve tissue oxygen supply. Hypoxia refers to a series of pathological changes that result in the changes of the body's functional metabolism and even morphological structure due to the insufficient supply of oxygen or use disorders. According to the reason of hypoxia and the change of blood oxygen, it is generally divided into four types.