At the end of expiration, the sound of foreign body impacting on the tracheal wall and subsonic area can be heard at the trachea, which is one of the symptoms of foreign body in the trachea. Later, the active foreign body moves with the airflow and can cause paroxysmal cough and dyspnea. The larynx has a rich distribution of nerves, and when stimulated by choking and other inadvertent foreign bodies, it produces a defensive firing cough, forcing the foreign body out, which plays a role in protecting the lower respiratory tract. Pediatric choking or throat tickling is more dangerous than adults. Since most of the foreign bodies in the respiratory tract are children, inhalation of foreign bodies, family members or not witnessed, and children can not tell themselves what happened. Foreign body inhalation history may not be asked, and children are often seen for wheezing and misdiagnosed as asthmatic bronchitis, or misdiagnosed as whooping cough due to paroxysmal choking, or misdiagnosed as pneumonia and bronchiectasis due to long-term respiratory infections. Therefore, for children with localized lesions in the lungs, which do not heal for a long time or sometimes offend, the so-called three unlike symptoms, that is, neither like tuberculosis, nor like typical bronchopneumonia, nor like other lung diseases, in this case, should be considered the possibility of foreign bodies in the respiratory tract, should be taken seriously, for detailed physical examination and X-ray examination is an important means of diagnosing foreign bodies. Due to the foreign body embedded in the bronchus and caused by different degrees of obstruction and different symptoms. 1.Incomplete obstruction of bronchus, the air can enter because of the expansion of trachea during inspiration, and less exhaled air because of the narrowing of bronchus during exhalation, which eventually leads to the increasing gas at the distal end of obstruction, forming obstructive emphysema. During the examination, it can be found that: ① the chest movement on the affected side is restricted during breathing; ② the breath sounds on the affected side are reduced, the fibrillation is weakened, and the percussion is drumming; ③ the heart and mediastinum are shifted to the healthy side on X-ray fluoroscopy, and the diaphragm is flat and unsupported. During respiratory activity, the heart and mediastinum oscillate, i.e., at the end of expiration, the heart and mediastinum shift to the healthy side. During inspiration, the heart and mediastinum move to the middle again due to the increase of pressure on the healthy side, and this phenomenon can be used to distinguish from obstructive pulmonary atelectasis. 2.The bronchus is completely obstructed and the air cannot pass during expiration and inspiration, then the air at the distal end of the obstruction is gradually absorbed by the lung and finally forms obstructive pulmonary atelectasis. On examination, it can be found that the respiratory movement on the affected side is restricted, the chest on the affected side is flat, the breath sounds are diminished or completely disappeared, the fibrillation is diminished, and the percussion on the affected side is turbid. x-ray fluoroscopy shows that the heart and mediastinum are displaced to the affected side and do not move with breathing, the diaphragm on the affected side rises, the rib space is reduced, and the lung shadow is denser.