The rib-diaphragm angle is the landmark position on radiographs when taking orthopantomographs of the chest, referring to the angle between the ribs and the diaphragm, which is normally at an acute angle and is relatively clear. Bilateral sharp angle of rib diaphragm indicates that the angle of rib diaphragm is normal, which means that there is no blood or fluid accumulation between the rib septum angles and no lesions such as adhesions of pleural tissues have occurred, so no special treatment is needed without too much tension. In the event of chest trauma, blood accumulation from chest bleeding will accumulate in the costo-diaphragmatic angle, resulting in the disappearance of the local acute angle. In case of pulmonary infection and pleurisy, there will be a significant accumulation of pleural fluid in the costo-diaphragmatic angle, leading to rounding of the costo-diaphragmatic angle and the occurrence of pleural adhesions. Further treatment such as hemostasis or anti-infection should be given according to the cause of the disease, and the effect of treatment should be further reviewed by frontal and lateral chest radiographs or chest CT.