Thoracentesis is one of the most basic operations performed by clinicians, in which the site of puncture is very important. The site of puncture varies because the gas and fluid to be extracted during puncture are different. Generally, whether in sitting, semi-recumbent or lying position, the gas in the thoracic cavity is located in the upper part, so the location of puncture is relatively fixed when puncturing the gas. The general position is located at the second intercostal space in the midclavicular line. When puncturing fluid, the puncture site varies due to the different positions of the patient. When the patient is in a sitting position for thoracentesis, the sixth and seventh intercostal spaces in the mid-axillary line are usually selected as the puncture sites, usually relying on the physician’s visualization, touch, percussion, and hearing, combined with chest radiographs and chest ultrasound. When the patient is in the prone or semi-prone position, the doctor’s vision, touch, percussion and hearing are also required for localization, but it is better to localize the puncture according to the ultrasound, or even to perform the puncture under the guidance of the ultrasound, which is safer.