1, tuberculosis, tuberculous pleurisy: tuberculosis mostly has systemic toxic symptoms, such as afternoon hypothermia, fatigue, night sweats, weight loss, insomnia, palpitations, etc., may be accompanied by hemoptysis symptoms, or as the first symptom, check the blood tuberculosis antibody positive, X-ray examination shows that the lesions are mostly in the upper lobes of both lungs, uneven density, polymorphic, multifocal, multi-calcification, few nodules aggregation, may have cavities or intrapulmonary dissemination, sputum can be found in the tuberculosis bacteria. The cytologic classification of the pleural fluid in tuberculous pleurisy is dominated by mononuclear cells, and the pleural fluid ADA is increased. 2, pleural effusion caused by heart failure: can be seen in patients with left ventricular failure, generally have other signs and symptoms of heart failure, such as progressive exertional dyspnea, telescopic breathing, nocturnal paroxysmal dyspnea, peripheral edema, jugular venous anger, bilateral pulmonary rales or gallop rhythm, heart failure symptoms improve, pleural effusion can mostly subside on its own. In addition to pleural effusion, there may be heart enlargement on chest X-ray. Pleural effusion is often bilateral and leaky. 3.Pleural effusion caused by hypoproteinemia: serum albumin is low, and the nature of pleural effusion is mostly leaky. 4.Malignant pleural effusion: Except for primary pleural mesothelioma, most of them are caused by metastasis of lung cancer, breast cancer and other parts of the tumor, most patients have no fever, chest tightness, shortness of breath, weakness, emaciation, fast progress of disease, pleural effusion is mostly bloody, LDH>200U/L, pleural fluid exfoliated cells, CEA and other tests can assist in diagnosis. 5, rheumatic immune disease caused by pleural effusion: rheumatoid arthritis and SLE and other connective tissue diseases can be complicated by pleural effusion, but the patient has obvious joint symptoms, pleural effusion is often a small amount, pleural fluid sugar content is very low, rheumatoid factor and other autoantibodies are often positive, may also be complicated by interstitial lung lesions. 6, pneumonia and pleural effusion: rapid onset, may have fever, chest pain, cough, cough, shortness of breath symptoms, X-ray examination with the presence of pneumonia, early pleural fluid more straw yellow, high white blood cells, mainly neutrophils, protein > 25g / l, pleural fluid smear and culture can find pathogenic bacteria, antibiotic treatment is effective. 7, lung abscess: rapid onset, high fever, coughing a lot of thick sputum, blood leukocytes and neutrophils increased, antibiotic treatment is effective. The cavity is mostly located in the lower lobe of the lung, the surrounding inflammatory infiltration is more serious, and there are often fluid planes in the cavity, while tuberculosis cavity mostly occurs in the upper lobe of the lung, the cavity wall is thinner, and there are fewer fluid planes in the cavity. 8, lymphoma: fever, emaciation, anemia, pleural involvement may appear pleural effusion, asymmetric enlargement of lymph nodes in the chest, often involving mediastinal lymph nodes. Lymph node and bone marrow aspiration can be helpful for diagnosis.