Objective To observe the clinical efficacy of Wenshen Xiaochuan Paste Recipe (WXPR) in preventing bronchial asthma, and to explore the mechanism. Methods Eighty patients were randomly divided into treatment group and control group. Each group had 40 patients. The control group was treated by conventional western medicine such as inhalation of steroid, and the treatment group was given oral use of WXPR based on the treatment for the control group. Treatment for both groups covered 60 days, and the follow-up lasted 10 months. The clinical outcomes included the clinical efficacy and immune indexes of peripheral blood T lymphocyte subsets CD3+, CD4+, CD8+and CD4+/CD8+ratio, and the serum IgE level. Results (1) After treatment and 12 months later, the scores of asthma control test (ACT ) in the two groups were increased obviously as compared with those before treatment, and there were statistically significant differences (P<0.05 or P<0.01) . The differences of ACT scores between the two groups were insignificant after treatment ( P>0.05) , but were significant ( P<0.05) 12 months later. (2) Within one year after treatment, the frequency of acute asthma attack was decreased in both groups (P<0.05 compared with that before treatment), and the treatment group had better effect on decreasing the attack frequency than the control group (P<0.05). (3) After treatment, the serum IgE, CD4+level, and CD4+/CD8+ ratio were decreased significantly, while CD8+ level was increased in the treatment group, and there were statistically significant differences ( P<0.05 compared with those before treatment). However, the differences of immune indexes in the control group were insignificant before and after treatment ( P>0.05). The improvement of immune indexes in the treatment group was superior to that in the control group ( P<0.05). Conclusion WXPR has good clinical efficacy in preventing and treating bronchial asthma. The mechanism is related with the inhibition of airway inflammation and improvement of immune function probably through regulating T lymphocyte subsets and lowering serum IgE level in asthma patients.