Fluid accumulation in the chest cavity refers to a type of disease in which the fluid retained in the pleural cavity exceeds the normal amount in the human body. According to the etiology, it can be generally categorized into exudative pleural effusion, leakage pleural effusion and injury-induced pleural effusion. 1. Exudative pleural effusion (1) Infectious pleural effusion: common in viral pneumonia, bacterial pneumonia, mycoplasma pneumonia and tuberculosis. (2) Cancer pleural effusion: pleural mesothelioma and metastatic pleural cancer. (3) Connective tissue diseases: such as systemic lupus erythematosus, dry syndrome, scleroderma and polymyositis. (4) Others: such as drug pleural disease, celiac disease, uremia, pulmonary embolism, post myocardial infarction syndrome. 2. Leaky pleural effusion: common in cardiac insufficiency, liver cirrhosis, nephrotic syndrome, glomerulonephritis, dialysis, hypoproteinemia, constrictive pericarditis, superior vena cava syndrome, mucous edema and other diseases. 3. Fluid accumulation in the thoracic cavity due to injury: ruptured aortic aneurysm, ruptured esophagus, ruptured thoracic duct, etc. It is recommended to go to the hospital for further diagnosis and treatment if there is fluid in the chest cavity.