The method of percussion of pleural effusion: the patient is seated and percusses from the 2nd intercostal space downward, when a turbid sound and a solid sound are detected, it means that there is pleural fluid from this intercostal space downward; then percusses from the 3rd and 4th intercostal spaces in the mid-axillary line downward, when a solid sound is detected, it means that there is pleural fluid from this area downward. The purpose of chest radiography is to see if the solid sound on percussion matches the site of hydrothorax on chest radiography, and if it does, the percussion is correct.