Diaphragmatic hypoplasia is a diagnostic imaging sign of emphysema, lung abscess, or tracheal foreign body on lung x-ray. Its etiology is commonly due to emphysema, lung abscess, or tracheal foreign body. Emphysema is a common cause of diaphragmatic hypoplasia. Emphysema is a very common chronic disease which also has a long course and brings great impact on people’s lives, and the incidence of emphysema has shown a rising trend in recent years. 1. Infection: This is one of the most noteworthy factors in the etiology of emphysema. Viruses, bacteria and mycoplasma are important factors in the acute exacerbation of this disease. Viruses are mainly influenza virus, rhinovirus, adenovirus and respiratory syncytial virus, etc.; bacterial infections with Streptococcus pneumoniae, Haemophilus influenzae, Cataplasma and Staphylococcus are common. 2, smoking: the most important cause of emphysema, tobacco contains tar, nicotine and hydrocyanic acid and other chemicals, can damage the airway epithelial cells, so that the cilia movement is reduced and macrophage phagocytosis; bronchial mucus gland hypertrophy, cupular cell hyperplasia, increased mucus secretion, so that the airway purification capacity is reduced; bronchial mucosa congestion edema, mucus accumulation, easy to secondary infection, chronic inflammation and smoking stimulation Submucosal receptors, so that the parasympathetic nerve function is hyperactive, causing bronchial smooth muscle contraction, airflow is restricted. 3, atmospheric pollution: harmful gases in the atmosphere such as sulfur dioxide, nitrogen dioxide, chlorine, etc. damage the airway mucosa and its cytotoxic effect, so that the cilia clearance function decreases, mucus secretion increases, increasing the conditions for bacterial infection, which is also one of the causes of emphysema. 4, dust and chemical substances: when occupational dust and chemical substances, such as smoke, allergens, industrial exhaust and indoor air pollution, etc., the concentration is too large or contact time is too long, all may produce emphysema unrelated to smoking.