The fishy smell in the sputum is due to the smell emanating from the sputum containing many inflammatory metabolites, the reason for which is mainly the inflammatory reaction of the respiratory tract, invasion by pathogens, and the exudation of purulent secretions from the respiratory tract mucosa, and congestion and edema of the mucosa is obvious. Inflammatory secretions of the respiratory tract contain a large number of live and dead pathogens, as well as a large number of exfoliated tissue fragments, dust and a large number of inflammatory metabolites, which are more common in clinical practice are infection to tuberculosis caused by Mycobacterium tuberculosis, bronchial lung cancer combined with obstructive pneumonia, with Pseudomonas aeruginosa, Staphylococcus aureus, Klebsiella can lead to fishy smell of sputum.