Inclusion Criteria:  age 4-14 years patients had mild to moderate persistent asthma. Patients have treated with low-dose inhaled corticosteroids (equivalent to Fluticasone propionate inhaled aerosol 250 ug/ day) combined with Leukotriene receptor antagonist (Montelulast) at least 6 months of and had no symptoms of asthma for nearly 3 months under well asthma control(Asthma Control Test (ACT) score more than or equal to 20). patients did not suffer from other acute or chronic diseases that may affect their growth and development  Exclusion Criteria:  patients with severe persistent asthma or mild persistent asthma failed to be well controlled by low-dose ICS after starting treatment suffer from other diseases: Congenital heart disease, chronic infectious disease, protracted diarrhea, congenital airway disease, congenital vascular ring malformation, congenital immune deficiency, tracheal foreign body, bronchial lymph node tuberculosis and gastroesophageal reflux etc. patients with poor compliance stop medication or fail to take medication on time.