Decreased diffusion function of the lungs reflects the dysfunction of the lung’s gas exchange, and when diffusion function is abnormal it often affects the body’s blood oxygen level. The degree of hypoxia can be insignificant due to the compensatory effect of the lung function. Patients often do not have obvious symptoms of shortness of breath, chest tightness or only slightly shortness of breath after physical activity, and the condition is not serious at this time. However, it is necessary to actively search for the cause of the disease and treat for the cause of the disease, such as chronic obstructive pulmonary disease, interstitial lung disease, pneumoconiosis, lung infections, tuberculosis and so on. The treatment of the primary cause can improve and delay the degree of diffusion function reduction, thus improving the patient’s prognosis. If there is no timely and effective treatment, the diffusion function of the lungs will further decline, and the patient will develop obvious wheezing, dyspnea, or even form a type 1 respiratory failure, at which time the disease becomes critical and the prognosis is poor.