Bacterial pneumonia is the most common type of infectious pneumonia. Diagnosis of bacterial pneumonia begins with the establishment of a pneumonia diagnosis. The diagnostic criteria are: 1. new onset of cough and sputum or aggravation of symptoms of pre-existing respiratory disease with purulent sputum with or without chest pain; 2. fever; 3. signs of solid lung changes and audible wet rales; 4. white blood cells >10×10^9/L or <4×10^9/L with or without left shift of nuclei; 5. chest X-ray showing lamellar or patchy infiltrative shadows or interstitial changes with or without pleural effusion. The diagnosis of pneumonia can be established after any one of the above items 1-4 plus item 5 and excluding tuberculosis, chest tumor, non-infectious interstitial disease, pulmonary edema, pulmonary atelectasis, pulmonary embolism, pulmonary eosinophilic infiltration and pulmonary vasculitis. The next step is to clarify that it is a bacterial infection and that calcitoninogen is increased in most common bacterial infections. Immunological and molecular biological methods can clarify atypical pathogenic infections, such as Legionella, mycoplasma, and chlamydia. Retaining qualified sputum specimens for culture before using antibiotics can help in early pathogenic diagnosis. However, sometimes in clinical practice, because the patient has been treated with antibiotics prior to consultation, relevant tests cannot clarify the bacterial infection, and diagnostic treatment methods can be used to clarify the diagnosis.