1. Local pain is the most obvious symptom of rib fracture, which is aggravated with coughing, deep breathing or body rotation. Sometimes patients can hear or feel bone friction themselves. 2. Pain and the destruction of chest stability will limit the mobility of breathing, make breathing shallow and fast, and reduce alveolar ventilation. Patients do not dare to cough, and the sputum stays, thus causing lower respiratory tract secretion obstruction, lung consolidation or atelectasis, which should be paid special attention to in elderly and frail patients or patients with original lung diseases. 3. Inhale when the flail chest exists, the negative pressure in the chest cavity increases, and the softened chest wall sinks inward; When exhaling, the chest pressure increases and the injured chest wall floats, which is contrary to the movement of other chest walls and is called "abnormal breathing movement". Abnormal respiratory movement can make the chest pressure on both sides unbalanced, and the mediastinum moves before and after breathing, which is called "mediastinal swing", which affects blood return and causes circulatory dysfunction, and is one of the important factors that lead to and aggravate shock.