Sharp bilateral rib diaphragm angle is an imaging term indicating that the rib diaphragm angle is acute and there is no accumulation of fluid or blood inside, therefore, sharp rib diaphragm angle is a normal phenomenon in chest radiographs and is a normal person’s performance. If the angle of the rib diaphragm is blunt, there is pleural fluid in the angle of the rib diaphragm, and if the angle of the rib diaphragm is blunt, it means that the accumulation of fluid in the pleural cavity has reached 500 ml. Therefore, by observing chest radiographs, whether the angle of the rib diaphragm is sharp or not can determine whether there is pleural effusion, and it can also be judged according to the thickening of the pleura in the angle of the rib diaphragm to determine whether there is pleurisy or not. When observing chest radiographs, when observing whether there is an effusion, the first thing to observe is the rib-diaphragm angle.