Diagnosis is based on history, physical examination, x-ray examination and pulmonary function measurements. x-ray examination shows increased anteroposterior diameter of the thoracic cavity, anterior protrusion of the sternum, widening of the posterior sternal space, low flattening of the diaphragm, decreased lung texture, increased lung field translucency, overhanging heart, widening of the pulmonary arteries and major branches, and small peripheral blood vessels. Pulmonary function measurements showed increased residual air and total lung volume, increased residual air/total lung volume ratio, significantly decreased 1-second rate, and decreased diffusion function. The electrocardiogram is generally abnormal, but sometimes it may show limb conduction low voltage. x-ray examination shows dilated thorax, widened rib space, parallel ribs, lowered and flattened diaphragm, and increased translucency in both lung fields. Respiratory function tests are important for the diagnosis of obstructive emphysema, with a residual air volume/total lung volume ratio >40%. In the presence of significant hypoxic carbon dioxide retention, arterial partial pressure of oxygen (PaO2) decreases and partial pressure of carbon dioxide (PaCO2) increases, and there may be a loss of compensatory respiratory acidosis with a decrease in pH. Blood and sputum examinations are generally unremarkable. Differential diagnosis with tuberculosis, lung tumors and occupational lung disease should be noted. In addition, chronic bronchitis, bronchial asthma and obstructive emphysema are all chronic obstructive pulmonary diseases, and both chronic bronchitis and bronchial asthma can be complicated by obstructive emphysema. However, the three are both related and different and cannot be equated. Chronic bronchitis is mainly limited to the bronchial tubes before the complication of emphysema, and there may be obstructive ventilation disorder, but the degree is mild, and the diffusion function is generally normal. During the exacerbation of bronchial asthma, there is obstructive ventilation and hyperinflation of the lungs, and gas distribution can be severely uneven. However, these changes are more reversible and respond better to inhaled bronchodilators. Diffusion dysfunction is also not obvious. Moreover, bronchial asthma is characterized by significantly higher airway reactivity and large diurnal fluctuations in lung function.