Moderate-to-severe asthma has a substantial impact on the health-related quality of life (HR-QOL) of the patients. Cordyceps sinensis is a traditional Chinese medicine that is evaluated clinically for the treatment of many diseases, such as chronic allograft nephropathy, diabetic kidney disease, and lung fibrosis. In order to investigate the effects of Cordyceps sinensis on patients with moderate-to-severe persistent asthma, 120 subjects were randomized to receive Corbin capsule containing Cordyceps sinensis for 3 months (treatment group, n = 60), whereas the control group (n = 60) did not receive treatment with Corbin capsule. Inhaled corticosteroid and as-needed β-agonists were used in the treatment of both groups. HR-QOL was measured with the Juniper's Asthma Quality of Life Questionnaire (AQLQ). The incidence of asthma exacerbation, pulmonary function testing, and serum measurements of inflammatory mediators were also evaluated. The results showed that the treatment group indicated a significant increase in AQLQ scores and lung function compared with the control group. The expression levels of the inflammation markers IgE, ICAM-1, IL-4, and MMP-9 in the serum were decreased and IgG increased in the treatment group compared with the control group. Therefore, the conclusion was reached that a formulation of Cordyceps sinensis improved the HR-QOL, asthma symptoms, lung function, and inflammatory profile of the patients with moderate-to-severe asthma. This trial is registered with ChiCTR-IPC-16008730.