ObjectiveTo evaluate the effect and safety of Buyang Huanwutang in treatment of connective tissue disease-associated pulmonary fibrosis in the patients with syndrome of Qi deficiency and blood stasis and explore the possible anti-fibrosis mechanism of Buyang Huanwutang. MethodSixty-six patients with connective tissue disease-associated pulmonary fibrosis with syndrome of Qi deficiency and blood stasis were randomized to receive either Buyang Huanwutang combined with routine therapy or routine therapy for 4 weeks. The primary outcome indicator was change in forced vital capacity （FVC） from the baseline， and the secondary outcome indicators included the changes in percentage of predicted forced vital capacity （FVC%pred）， percentage of forced expiratory volume in first second to predicted value （FEV₁%pred）， King's Brief Interstitial Lung Disease （K-BILD） total score， 6 minute walking distance （6MWD）， hydroxyproline （HYP）， matrix metalloproteinase （MMP）， tissue inhibitor of metalloproteinase-1 （TIMP-1）， and transforming growth factor-β （TGF-β） from baseline. Patients in line with the inclusion criteria were included in the primary analysis， and sensitivity analysis was performed after multiple imputation of missing data. Safety set was adopted for safety analysis. ResultThe 66 patients （included in the sensitivity analysis） meeting the inclusion criteria included 34 in the observation group and 32 in the control group， and 60 patients finally received the whole trial intervention （included for primary analysis）. Compared with the baseline， the FVC increased in the observation group and decreased in the control group after intervention （P<0.01）， which was consistent between the sensitivity analysis and the primary analysis. The changes in FVC%pred， FEV₁%pred， 6MWD， and K-BILD total score from baseline in the observation group were superior to those in the control group （P<0.01）， with consistent results between the sensitivity analysis and the primary analysis. TIMP-1 in the observation group decreased compared with baseline （P<0.05）， while TIMP-1 in the two groups showed no significant changes from the baseline The observation group outperformed the control group in the changes in HYP， MMP-9， and TGF-β from baseline （P<0.05）. The common adverse events were cough， diarrhea， nausea， rash， and upper gastrointestinal tract infection， the incidence of which showed no statistical difference between the two groups. ConclusionBuyang Huanwutang can improve lung function， motor function， and quality of life in patients with connective tissue disease-associated pulmonary fibrosis and has good safety. The mechanism may be related to the reduction of TGF-β， MMP-9， and TIMP-1 levels and maintaining of MMP-9/TIMP-1 balance.