Many clinical conditions can cause a decrease in blood oxygen, such as severe pneumonia, chronic obstructive pulmonary disease, bronchiectasis, tuberculosis, lung tumors, etc. The normal partial pressure of blood oxygen is 75-100 mmHg, if it is lower than 75 mmHg, it is clinically diagnosed as hypoxemia. Patients with hypoxemia should be treated with symptomatic oxygen therapy, and the relevant tests should be completed to clarify what kind of disease is causing the lowering of blood oxygen. Patients with reduced blood oxygen due to severe pneumonia require aggressive anti-infective therapy. When the patient’s oxygen level is reduced due to cardiac insufficiency, anti-heart failure treatment is required. When the patient’s oxygen is reduced due to tuberculosis or tumor, anti-tuberculosis and anti-tumor treatment is required.