Thoracentesis passes through the layers of skin, subcutaneous tissue, fat, chest wall muscles, intercostal muscles, wall pleura, and then enters the thoracic cavity, in the process of puncture, after encountering a sense of emptiness, it indicates that it has entered the thoracic cavity, and further puncture is avoided in order to prevent puncturing the lungs, which may cause lung leakage and other undesirable symptoms. The purpose of thoracocentesis is to diagnose or treat diseases, such as pleural effusion by thoracocentesis to extract fluid, do the tests of pleural fluid, pleural fluid routine, pleural fluid biochemistry and other tests, to clarify the nature of the pleural effusion, what causes it, and then targeted treatment.