Sputum is mostly seen in infectious diseases of the lower respiratory tract, including acute bronchitis, chronic bronchitis, bronchial asthma, chronic obstructive pulmonary disease, bronchiectasis, tuberculosis, and pulmonary fibrosis with infection. Sputum is mainly due to secretions that appear after infection of the lower respiratory tract, combined with dust in the air and expelled from the respiratory tract. Once clinical symptoms of spitting up appear, lower respiratory tract infections, including viral bacterial, mycoplasma, chlamydia, fungal, tuberculosis and other infections, are mostly considered. Therefore, when symptoms of spitting up appear, patients are advised to have chest X-ray or chest CT examination to further clarify the source of sputum and whether it is a manifestation of respiratory tract infection, tuberculosis, tumor, etc. Patients with spitting up sputum are seen in addition to long-term smoking and dusty work, including jobs such as masonry, coal mining, chef, hairdresser, etc. It can also be seen in lower respiratory tract infections, and chest imaging needs to be given to further clarify the diagnosis.