When pleural effusion is examined on chest X-ray, depending on the amount of effusion, the chest X-ray will show different manifestations, which may vary from no manifestation to mediastinal diaphragm compression and displacement. 1. When the amount of pleural effusion is less than 300 milliliters, the chest X-ray usually does not show any abnormality. 2. When the volume of pleural effusion exceeds 300 ml, if the fluid is confined under the 4th anterior rib on the standing chest X-ray, it is a small amount of fluid, and the angle of the rib-diaphragm can be seen to become obtuse or disappear. 3. If the amount of effusion further increases and the standing chest radiograph shows that the effusion is above the 4th anterior rib and confined below the 2nd anterior rib, it is a moderate amount of effusion, and the upper edge of the fluid on the chest radiograph is high on the outside and low on the inside, which shows a curved concave surface. 4. If the amount of effusion exceeds the 2nd anterior rib on the chest radiograph, it is a large amount of effusion, at this time, the lung field on the side of the effusion shows dense shadow, the diaphragm decreases, and the mediastinum is passively shifted to the healthy side. There are also some cases of limited pleural effusion, such as encapsulated effusion and interlobar effusion, in which the effusion is confined to some parts of the lungs, and a localized hyperdense shadow is seen. When the chest X-ray suggests pleural effusion, it is necessary to go to the hospital for regular medical examination and treatment.