Objective：To investigate the clinical efficacy of vitamin D in the adjuvant treatment of bronchial asthma in children. To investigate the correlation between vitamin D levels and various biological indicators of asthma in children with bronchial asthma. Methods：279 children with initial diagnosis of bronchial asthma were recruited as study subjects. Various clinical and biological indicators were detected at the first visit of children. All subjects were grouped and compared according to the initial vitamin D level. Then，children with low serum vitamin D level were randomly divided into the treatment group and the control group. On the basis of the conventional treatment for asthma，the treatment group was given vitamin D supplementation of 400-800 IU/ day orally，and the differences between the two groups in the proportion of patients with acute asthma attacks，the level of asthma control and the number of unsuccessful step-down treatment were compared. Results：The mean proportion of eosinophil in the low vitamin D group was significantly higher than that of the normal group［（4.46±3.92）% vs. （3.46±2.61）%，P < 0.05）］. During the 1-year follow-up，the proportion of acute asthma attacks，the level of asthma control and the number of unsuccessful step-down treatments in the experimental group were not significantly improved compared with those in the control group. Even within 3 months of treatment，the proportion of children in the experimental group with acute asthma attacks was significantly higher than that in the control group［37.3% vs. 12.5%，P < 0.05］. Conclusion：Among children with bronchial asthma，children with low vitamin D levels may be more susceptible to allergies. Vitamin D supplementation in children with bronchial asthma has no significant effect on asthma symptom control and may even increase the risk of acute asthma attacks.