Bronchial asthma is a suppressive disease characterized by chronic airway inflammation and airway hyperresponsiveness, with recurrent episodes of wheezing, coughing, shortness of breath, and chest tightness as the main clinical manifestations, often attacking and intensifying at night or in the early morning. During bronchial asthma attacks in children, scattered or diffuse expiratory phase dominated croup can be heard in both lungs, and the expiratory phase is prolonged. The manifestation and severity of respiratory symptoms are characterized by changes over time and are often accompanied by variable expiratory airflow limitation, such as the respiratory symptoms of typical asthma, which have the following characteristics: 1. Diversity of triggers: there are often triggers such as marginal exposure to upper respiratory tract infection, strenuous exercise, laughing, crying, and climate change; 2. Recurrent episodes: sudden onset or exacerbation of episodes when triggers are encountered; 3. Time Rhythmical: often attack or aggravate at night and in the early morning; 4. Seasonal: often attack or aggravate in autumn and winter or during the change of season; 5. Reversible: asthma medication can usually relieve the symptoms, and there can be a significant remission period. The most common abnormal sign in children with asthma is expiratory phase croup, while in chronic persistent and clinical remission patients may have no abnormal signs. In acute exacerbations of severe asthma, due to severe airway obstruction, breath sounds may be significantly reduced and croup may instead be diminished or even absent, called silent lung, when signs associated with respiratory failure are usually present and even life-threatening. Pulmonary function in children with asthma is characterized by variable airflow limitation and increased airway responsiveness.