If there is a small amount of fluid accumulation in the pleural cavity, and the volume of fluid is <300ml, it is called a small pleural effusion. There are many reasons for small pleural effusion, including tuberculous pleural effusion, pneumonic pleural effusion, malignant pleural effusion and so on. 1. Tuberculous pleural effusion: the common cause is tuberculous pleurisy, mostly seen in adolescents, with clinical manifestations of chest pain and tuberculosis poisoning symptoms. The clinical manifestation is chest pain with symptoms of tuberculosis toxicity. It is necessary to carry out fluid extraction, which can relieve the clinical symptoms. Anti-tuberculosis drugs such as isoniazid, rifampicin and ethambutol can be taken as prescribed by the doctor. 2. Pneumonic pleural effusion: pleural effusion caused by pneumonia, lung abscess and bronchodilator infection, usually due to the involvement of pneumonia in the pleura, commonly found in the elderly and weak, immunocompromised people, patients often have fever, cough, chest pain and other manifestations. Once diagnosed, thoracentesis should be performed as soon as possible to check the routine of pleural fluid and decide whether to drain by intubation. 3. Malignant pleural effusion: it is mainly caused by direct invasion or metastasis of lung cancer, breast cancer and lymphoma to pleura, and it is more common in middle-aged and old people. The primary malignant disease is controlled by drugs, including systemic chemotherapy and targeted therapy. If there is a small amount of fluid in the pleural cavity, it is recommended to go to the hospital in time to clarify the cause of the disease and then be treated under the guidance of the doctor.