Thoracentesis is one of the common operations in clinical practice, and the main steps and precautions are as follows: i. Locate the location of the puncture site by ultrasound, and local lidocaine infiltration anesthesia. Second, a small incision of 2 mm of skin is cut, and the puncture needle slowly enters the thoracic cavity under ultrasound guidance, and the retraction of fluid indicates successful puncture, and 50 ml of pleural fluid is retained for routine, biochemical and bacterial culture examination. Third, for patients with more fluid in the chest cavity, a drainage tube can be left in place for chest drainage, and the drainage flow should be controlled at about 600ml on the first day to avoid uncomfortable symptoms for patients. Fourth, patients with indwelling drains need to be properly fixed to avoid folding and twisting of the drainage tube to affect the drainage effect. Fifth, if the patient has no drainage fluid from the chest drainage, it can be checked by ultrasound, and the pleural fluid needs to be removed as soon as possible to avoid local infection.