There is no clinical indicator of respiratory capacity. Clinical determination of respiratory capacity can be done by measuring spirometry and exertion spirometry. Respiratory function measurement is a common test for asthma, COPD, pulmonary fibrosis and other diseases, and the common indicators of pulmonary function measurement include spirometry VC, exertion spirometry FVC, first-second exertion expiratory volume FEV1, and other indexes to decide. The average lung volume of normal people is 2500ml~3500ml; the FVC is often used in conjunction with the first second expiratory volume FEV1. For obstructive lung diseases such as asthma and COPD, FEV1/FVC is usually decreased; while for restrictive lung diseases such as pulmonary fibrosis, FEV1/FVC may be normal or increased. If the above indicators are abnormal, it is recommended to go to the hospital in time to improve the evaluation, and follow the doctor’s instructions for reasonable and standardized treatment after a clear diagnosis.