Objective:To investigate the efficacy of Qingfei Yihuo Capsules(清肺抑火胶囊,QYCs) in preventing the air pollution associated exacerbation of chronic obstructive pulmonary disease (COPD).Methods:This was a prospective,parallel,single-blind,randomized,placebo-controlled trial.Sixty patients with stable Group D COPD were randomly allocated to receive either oral QYCs (intervention group) or placebos (control group,30 cases per group) for 15 days in the presumed high-incidence air pollution season and followed-up for 1 year.Both groups were given individualized Western medicine therapy according to the Global Initiative for Chronic Obstructive Lung Disease criteria as usual.Total and separate numbers of acute exacerbation (AE)associated with striking air pollution was the primary outcomes.Secondary outcomes included total numbers of deteriorating respiratory symptoms and separate numbers associated with striking air pollution,as well as scores of COPD Assessment Test (CAT) and modified Medical Research Council Scale (mMRC).Results:All the 60 patients completed the study.There was no statistical significance in total numbers of AE between the two groups (P＞0.05).Compared with the control group,a significant reduction in air-pollution associated numbers of deteriorated respiratory symptoms was observed in the intervention group (1.9 ± 1.2 vs.3.6 ± 2.4,P＜0.01).At the end of follow-up,there was no significant difference in CAT and mMRC scores between the two groups (P＞0.05).Only 2 patients in the intervention group reported diarrhea and recovered after drug discontinuance.Conclusion:For patients with Group D COPD,oral QYCs in high-incidence season of air pollution can effectively mitigate respiratory symptoms associated with air pollution,although there was no evidence that it had a significant reductive effect on AEs.(Registered at Chinese Clinical Trial Registry,registration No.ChiCTR-IOR-17013827)