The most common opportunistic infection in AIDS is Pneumocystis pneumonia. When patients enter the AIDS stage, they are prone to opportunistic infections because the CD4+ T-lymphocyte count drops to a very low level, and many patients can be infected with Pneumocystis at this time. Pneumocystis belongs to a kind of fungus, and after infection, chronic cough, fever and dyspnea can appear, and very typical manifestations can be seen through chest CT, and Pneumocystis can be found through sputum examination and alveolar lavage fluid examination for diagnosis.