Bronchial asthma is one of the most common inflammatory airway disorders. As one of the main non-drug therapies, the Sanfu herbal patch (SHP) has been widely used to treat bronchial asthma, although the evidence for its efficacy and associated mechanism are inconclusive. The objective of this trial is to clarify the clinical efficacy and safety of the SHP in the treatment of bronchial asthma in the chronic persistent or clinical remission stage and to provide high-quality data for further research. We propose a multicentre, double-blinded, parallel, randomized, placebo-controlled clinical trial involving 4 study hospitals in China. A total of 72 eligible participants will be randomized into an SHP group and a placebo group. They will receive an SHP for 3 treatment sessions. The primary outcome will be changes in forced expiratory volume in 1 s after 3 treatment sessions. Secondary outcomes will include the following: (1) the Asthma Quality of Life Questionnaire, Asthma Control Test, and Asthma Long-term Follow-up Scale; (2) levels of Metallothionein-2 and Transgelin-2 in blood and urine; and (3) levels of IL-5, IL-13, IL-23, IL-25, and thymic stromal lymphopoietin in blood. Analysis of the data will be performed at baseline, at the end of the 2nd and 3rd treatment sessions, and at the 24-week follow-up. The safety of the SHP will be evaluated at each treatment session. The aims of this trial are to determine whether the SHP is more effective than placebo in the treatment of patients with bronchial asthma, as well as whether the SHP works by reducing airway inflammation and reversing bronchoconstriction. Chinese Clinical Trial Registry ( http://www.chictr.org.cn ), ChiCTR1900024616. Registered on 19 July 2019.