Etiologies to be identified 1. Primary immunodeficiency diseases: These include primary antibody deficiency diseases, cellular immunodeficiency diseases, combined immunodeficiency diseases, complement deficiency diseases, phagocytosis deficiency diseases, and other primary immunodeficiency diseases. 2. Congenital abnormalities in lung parenchyma and pulmonary vascular development: Children with congenital abnormalities in lung parenchyma development, such as pulmonary isolation disease and pulmonary cyst, are prone to recurrent pneumonia or chronic pneumonia. Abnormal pulmonary vascular development leads to pulmonary stasis or ischemia, which is prone to co-infection and causes recurrent pneumonia. 3, congenital abnormalities of airway development: such as tracheobronchial stenosis, tracheobronchial softening, tracheobronchial bridges, these malformations often cause obstruction of airway secretions and recurrent pneumonia. 4, congenital heart malformations: Various congenital heart diseases, especially the left-to-right shunt type, can cause recurrent pneumonia due to pulmonary stasis. 5, primary ciliary dyskinesia: cilia structure or dysfunction, due to respiratory mucus clearance obstacles, pathogenic microorganisms retained in the respiratory tract easily lead to recurrent pneumonia or chronic pneumonia. 6, cystic fibrosis: In western countries, cystic fibrosis is the most common cause of recurrent pneumonia in children. Oriental yellow race rare, China’s mainland and Taiwan have reported individual cases in children, suggesting the possibility of this disease in our children. 7, intra-airway obstruction or extra-tubular compression: The most common disease causing intra-airway obstruction in children is bronchial foreign body, followed by tuberculous granuloma and caseous material obstruction, and occasionally tracheal and bronchial primary tumors. The causes of extra-osseous compression of the airway are mostly mediastinal, tracheobronchial lymph node tuberculosis, tumors, and vascular malformations. 8, bronchial dilatation: confined or extensive bronchial dilatation caused by various reasons, due to impaired clearance of secretions, may recurrently occur pneumonia. Repeated aspiration: Repeated aspiration in children with swallowing dysfunction such as mental retardation, delayed cricopharyngeal muscle development, neuromuscular disease, and children with gastroesophageal reflux can lead to repeated pneumonia due to repeated aspiration.