Long-term oxygen therapy is a basic therapy for patients with chronic respiratory system chronic hypoxia. It is mainly used for patients with chronic obstructive pulmonary emphysema with PaO2<7.3kPa (55mmHg), with erythrocytosis, or pulmonary heart disease, or pulmonary arterial hypertension. The method is: nasal cannula method 3L/min, or other methods can be used, 15 hours a day, 3 weeks of continuous oxygen inhalation. Clinical observation can correct long-term hypoxia; improve vital signs; reduce the occurrence of erythrocytosis; improve sleep and nocturnal hypoxia; help the recovery of spirit and energy; improve the general condition. However, attention should be paid to the indications, oxygen administration concentration and oxygen administration amount to prevent oxygen toxicity. The main effects of oxygen therapy include: 1.Reducing hypoxemia: When PaO2 reaches above 60mmHg and SaO2 reaches 85%-90%, it can basically meet the needs of tissue metabolism. 2.Ease the pulmonary hypertension caused by hypoxia, reduce erythrocytosis, lower blood viscosity, reduce the burden on the right ventricle, and delay the development of pulmonary heart disease. 3.Oxygen inhalation can relieve bronchospasm, reduce respiratory distress and improve ventilation dysfunction. 4.Improve the physical condition of patients, improve sleep and brain function, improve exercise endurance and quality of life. 5.Improve the prognosis of patients with chronic obstructive pulmonary disease and prolong life. 6.Reduce the number of hospitalization and save medical cost.