The differential diagnosis of lung infection is tuberculosis, lung cancer, bronchiectasis, etc. Most of the lung infections are caused by bacterial, viral, fungal, and mycoplasma infections, and the symptoms are coughing, coughing up sputum, fever, and in severe cases, dyspnea. It can be diagnosed by chest X-ray. Treatment requires the use of sensitive antibiotics to fight infection. The differential diagnosis is analyzed as follows: 1. Tuberculosis and lung infection have the same symptoms of cough, sputum and fever. However, TB is mostly characterized by low-grade fever, as well as night sweats, lethargy, fatigue, and hemoptysis. Chest X-ray and tuberculin test can be used to make the initial diagnosis for lesions that develop in the apices of the lungs. Finding tubercle bacilli in sputum can confirm the diagnosis. 2. The difference between lung cancer and lung infection is that lung cancer cough is mostly irritating dry cough without sputum and hemoptysis. Most of them are old people and antibiotic treatment is ineffective. They are diagnosed by chest CT and fiberoptic bronchoscopy and other examinations. 3. The symptoms of bronchiectasis and lung infection are different. Bronchiectasis coughs up sputum with a large amount of purulent sputum, and there will also be high fever, dyspnea and other symptoms. Chest X-ray shows fluid level.