A blunted rib diaphragm angle means that there is fluid in the pleural cavity. There are several possible types of fluid in the pleural cavity: first, bloody fluid; second, exudate; and third, leaky fluid. In the case of hemorrhagic fluid, if the pleural cavity cannot be absorbed after a period of time, the hemorrhagic fluid may crust, and after crusting, a relatively hard crust will be formed in the pleural cavity, which leads to a difficult medical topic called hypothorax, which extremely affects the thoracic movement and also affects the person’s breathing. In addition, if there is exudate or leakage, the protein content of exudate is low and can be absorbed easily, while leakage may be purulent or have a high protein content, which may also form a shackle chest. It is recommended to check the CT early if the angle of the rib diaphragm is blunt to identify the nature of the pleural effusion.