Left upper lobe atelectasis is a more serious condition in which the volume or air content of the left upper lobe of the lung is reduced and is characterized by symptoms such as chest tightness, shortness of breath, dyspnea, and dry cough. Left upper lobe atelectasis can be categorized as either congenital or acquired. Congenital is mostly seen in infants and acquired is mostly seen in adults. Acquired left upper lobe atelectasis can be caused by a variety of reasons, common causes include bronchial secretion of thick fluid to form mucus plugs, tumors, granulomas or foreign bodies caused by bronchial lumen obstruction. The severity of left upper lobe atelectasis is mainly related to the cause of the disease, the degree of atelectasis, the time of occurrence, and complications. If the onset of the disease is more acute, and when combined with infection, it manifests as chest pain on the affected side, sudden dyspnea, cyanosis, chills, fever and other symptoms, and the condition is critical and requires timely treatment. It is recommended that the patient go to the hospital in time, clarify the cause of the disease, and actively treat it, so as not to delay the condition.