Pleural effusion is a common disease in thoracic surgery, and the cause of pleural effusion in China accounts for the largest proportion of tuberculosis, 54.5%, and cancer accounts for 23.1%, while in the West cancer accounts for almost half, while tuberculosis accounts for only 10%. Diagnosis of malignant pleural effusion: 1. The value of enhanced chest CT: the specificity of circumferential pleural thickening, nodular pleural thickening, mural pleural thickening greater than 1 cm, and mediastinal pleural thickening in diagnosing malignant pleural effusion is 100%, 94%, 94% and 88% respectively. The sensitivity was 41%, 51%, 36% and 56%. 2, the value of PET-CT: sensitivity of about 93%, specificity of about 80%; reasons for false positives: uremic pleural fluid, parapneumonic effusion, after using talc fixation; if the pleural fluid cytology is negative, and PET-CT is also negative, malignant pleural fluid can be initially excluded; it can be used to judge the efficacy of pleural mesothelioma. 3.Blind pleural biopsy is not as valuable as pleural fluid cytology for the diagnosis of malignant pleural fluid (44% vs. 62%), but the positive rate of pleural biopsy under direct medical thoracoscopy can reach 95%. 4, the diagnostic value of enzymatic and tumor markers in pleural fluid: (1) LDH: pleural fluid LDH / serum LDH > 3, can basically determine malignant pleural fluid. (2) CEA: sensitivity 50%, specificity 99%, mostly seen in adenocarcinoma. (3) Telomerase activity assay: currently considered superior to CEA (4) CA125: increased in adenocarcinoma and mesothelioma (5) CYFRA21-1, mainly in squamous carcinoma. (5) DNA multiplication test of tumor cells in pleural fluid. If the etiology cannot be clarified, the thoracoscopic pleural biopsy carried out by our department helps to solve this problem. Treatment of malignant pleural fluid: 1, intrathoracic perfusion drugs: currently commonly used talc, thrombin, tetracycline, cisplatin, carboplatin, mitomycin, domestic also use interleukin 2, tumor necrosis factor, short small rod-shaped bacillus, mushroom polysaccharide, high polysaccharide, etc. 2.Molecular targeted therapy: Because of the high rate of EGFR mutation in patients with adenocarcinoma combined with malignant pleural fluid. So ERSA and Troche oral can sometimes control pleural fluid or pericardial effusion very well. 3.Anti-vascular survival drugs: Endo, bevacizumab have encouraging effect on hemorrhagic pleural fluid. 4.Chemotherapy: systemic chemotherapy is effective in controlling pleural fluid in breast cancer, small cell lung cancer, lymphoma, ovarian cancer, and pemetrexed chemotherapy is effective in controlling pleural fluid in lung adenocarcinoma.