The common reasons for small lung capacity are as follows: 1, physiological factors: such as small thorax, lack of exercise. In different stages of human growth and development, lung capacity varies, adult stage lung capacity is about 3500mL, some people may be low, in 1000-2000mL, at this time you need to find out the reason, may be due to inept exercise, lack of exercise, resulting in poor whole body motor function state, which leads to low lung capacity; 2, pathological factors: such as lung solid changes, pleurisy, thoracic Pathologic factors: such as solid lung changes, pleurisy, thoracic deformity, etc., can make the lung capacity of the patient become smaller. If the patient’s thoracic development is deformed due to calcium deficiency, such as chicken breast, which restricts the expansion of the lungs, the lung capacity will be reduced. Also, some patients may contract lung diseases, such as tuberculosis and lobar pneumonia, which cause extensive fibrosis and solid lesions in the lungs, leading to a reduction in lung capacity. In addition, patients may have reduced lung volumes due to occupational diseases, including pneumoconiosis and asbestosis. Therefore, there are more reasons why a patient may have small lung volumes, and a follow-up history with CT and chest radiographs of the lungs can identify the cause.