The change from white sputum to yellow sputum in pneumonia usually indicates that the patient has a secondary bacterial infection or the original bacterial infection in the lung has not been effectively controlled, and some patients may also cough yellow sputum due to secondary complications. For example, patients with viral pneumonia can sometimes cough up a small amount of white mucous sputum, but such patients have decreased resistance and are prone to cough up pus sputum secondary to mixed bacterial lung infections. It is also possible that the degree of lung infection is further aggravated because the existing bacterial pneumonia is not effectively treated with anti-infection in a timely manner, and the coughing of white mucous sputum becomes purulent sputum. In some patients, due to the difficulty in controlling the lung inflammation, lung abscess may be formed secondary to it, and the amount of pus-coughing sputum may also increase. Therefore, in this case, we should review blood routine, sputum culture, sputum fungal smear, sputum tuberculosis smear, review lung CT and other related examinations in a timely manner, and add corresponding anti-infection and expectorant treatment to control the degree of lung infection as soon as possible according to the original cause.