The anatomical classification of pneumonia, such as “lobar”, “lobular”, and “interstitial”, has not been adapted to subsequent changes in clinical conditions. The change and diversification of pneumonia etiology, atypical clinical manifestations, discovery of new pathogenic microorganisms and epidemiological trends. Judging from the perspective of treatment and patient prognosis, pneumonia should be classified by etiology, and it is very important to emphasize the etiologic diagnosis. However, in clinical practice, it is often easier to make a diagnosis of pneumonia and quite difficult to make an etiologic diagnosis of pneumonia. The classification of pneumonia into two categories, “community-acquired pneumonia” and “hospital-acquired pneumonia”, according to the place of infection acquisition, reflects the differences in the environment of onset, source of infection, composition of pathogens, population and direction of treatment. The classification is simple, clinically useful, and reflects the differences in the setting, source of infection, pathogen composition, population, and treatment direction. The classification is simple, clinically useful, and has been accepted by most scholars for its convenience in terms of pneumonia pathogenesis, empirical selection of antibiotics, and estimation of patient prognosis. The main difference between the two types of pneumonia is whether the patient’s pulmonary infection is acquired during hospitalization; therefore, pneumonia that is in the incubation period is admitted to the hospital and occurs after hospitalization should be community-acquired pneumonia, while pneumonia that occurs only after discharge from the hospital is acquired in the hospital should be hospital-acquired pneumonia, and the average incubation period of most bacterial infections does not exceed 48 hours, so pneumonia that occurs after 48 hours of hospitalization is considered hospital-acquired pneumonia. The prominent features of community-acquired pneumonia and hospital-acquired pneumonia are: 1. The former occurs mostly in healthy people, and the latter occurs mostly in people with underlying diseases; 2. The former is more common with gram-positive cocci, and the latter with gram-negative bacilli; 3. The former has a more typical clinical presentation, and the latter often has an atypical clinical presentation. However, this classification method is only preliminary and generalized. It is not a substitute for etiological classification, rather, it is more important to promote and strengthen the research of etiological diagnosis.