The diagnosis is easily confirmed by the lack of systemic symptoms such as fever and the horizontal turbid sound on percussion. However, it must be distinguished from pleurisy. Pleurisy has fever, chest pain, cough, pleural friction sound, mostly occurs on one side, pleurisy is exudate, contains a large amount of fibrin and protein, Levatra’s reaction is positive. In contrast, pleural fluid has no systemic symptoms, and the fluid in the chest cavity is leaking fluid, which is relatively clear and thin, containing a small amount of fibrin and protein, with a negative Levata’s reaction. Differential diagnosis of exudative pleural fluid: 1. Leaky (hydrothorax) pleural fluid when congestive heart failure, nephrotic syndrome, liver cirrhosis and other formation of hypoproteinemia resulting in reduced colloid osmotic pressure and water and steel retention and cause pleural fluid; any cause of superior vena cava obstruction, the occurrence of leaking pleural fluid; part of the disease causing ascites, through the diaphragm lymphatic drainage into the chest cavity caused by pleural fluid. Clinical manifestations include cough, chest distension, shortness of breath and manifestations of the original disease, and signs of pleural effusion on physical examination. Pleural fluid is non-transparent, relative density <1.016, protein content below 30g/L, the ratio of pleural fluid and serum protein amount is less than 0.5; lactate dehydrogenase of pleural fluid is less than 200U/L, the ratio of lactate dehydrogenase of pleural fluid and serum is less than 0.6; glucose content is similar to blood glucose; leukocytes in pleural fluid are often completely work than 1X10/L, no pathogenic bacteria. 2, tuberculous pleural effusion tuberculous Pleurisy is a highly allergic reaction of the organism to the protein component of the tuberculosis bacillus, as a consequence of primary infection or secondary tuberculosis involving the pleural membrane in children and adolescents. The clinical onset can be acute or gradual, with fever, chest pain, dry cough, along with symptoms of tuberculosis toxicity such as fatigue, emaciation, lack of appetite, and night sweats. In the dry pleuritis stage, chest pain increases with deep breathing and coughing, and pleural friction sounds are important signs. As the amount of pleural fluid increases, the patient gradually feels short of breath, the pleural fluid is straw yellow transparent or boat cloudy, hairy glassy, after more liberation the fluid can be dark yellow mixed, the relative density of pleural fluid is often above 1.016, the total number of leukocytes is 1~2X10/L, the acute stage is dominated by neutrophils, the chronic stage is dominated by lymphocytes, mesothelial cells are generally less than 1%. The protein content was above 25g/L, and the sugar content was mostly below 2.8mmol/L; lysozyme and adenosine deaminase in pleural fluid were increased; TB bacilli were easily found in pleural fluid smear and collection, and about 1/3 of the culture method was positive. Pleural biopsy 1/2 cases can see case or non-case granuloma tissue, when the pleura has inflammatory adhesions, it can form encapsulated pleural effusion. 3, malignant pleural effusion primary cancer is mainly lung cancer and breast cancer, followed by lymphoma; a few are ovarian cancer, gastric cancer, uterine tumors, etc. The direct mechanism of tumor-induced pleural effusion includes pleural metastasis, which increases vascular permeability; obstruction of pleural lymphatic drainage, mediastinal lymph nodes obstruction of lymphatic return; obstruction of thoracic duct; obstruction of bronchial gas to reduce pleural cavity pressure; pericardial involvement (elevated vascular hydrostatic pressure, producing leakage fluid.) The sound connection mechanisms are hypoproteinemia, obstructive pneumonia, pulmonary embolism, and complications of radiation therapy. In addition to many symptoms of tumor itself, malignant pleural effusion is often associated with shortness of breath, emaciation, chest pain, weakness and poor circulation. x-ray examination can be seen from small amount to whole pleural effusion, and when the amount of effusion is large, the shadow of tumor in the lung and mediastinal lymph nodes is often not easy to recognize, then CT examination can show the lesion. Malignant pleural fluid is often bloody and grows rapidly after fluid extraction. Chest fluid examination includes routine, cytology, enzymatic changes, carcinoembryonic antigen, etc. Finding cancer cells in the pleural fluid is the basis for confirming the diagnosis of malignant pleural effusion. Since the cancer is mostly located in the dirty pleura first, while it may only be scattered in the wall pleura, the positive rate of pleural biopsy is not high.