Yellow sputum is a common manifestation of problems in the respiratory system, usually due to a sticky substance secreted by the trachea, bronchus, nasal cavity and other tissues of the trachea after respiratory system lesions. It is commonly found in chronic bronchitis, bronchial dilatation, lung abscess, pneumonia and other diseases, and the specific causes are analyzed as follows: 1. Chronic bronchitis: it is a chronic non-specific inflammation of the trachea, bronchial mucosa and surrounding tissues, which is clinically common in Streptococcus pneumoniae, Haemophilus influenzae, Cataplasma, Staphylococcus and other infections, manifested as coughing up sputum, coughing or accompanied by wheezing and other symptoms; 2. Bronchial dilatation: the patient’s Bronchial wall structure has been destroyed, irreversible bronchial expansion and deformation, usually combined with Gram-negative bacillus infection, such as Pseudomonas aeruginosa, Haemophilus influenzae, Klebsiella pneumoniae, etc., patients will have more yellow pus sputum, repeated cough, repeated hemoptysis, etc.; 3, lung abscess: mostly caused by Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae and other pathogenic bacteria of the lung Purulent inflammation, lung tissue necrosis liquefies and forms cavities, if the infection is not controlled in time, the symptoms can intensify, and the patient’s lungs are stimulated by a large amount of pus, resulting in coughing up large amounts of yellow sputum; 4. Pneumonia: Mostly the alveoli are infected with Streptococcus pneumoniae, Staphylococcus, etc., which damage the lung tissue and produce pus, and the patient has the symptoms of coughing up yellow sputum, and the patient will have other symptoms such as fever, chills and cough.