This paper mainly aimed to establish an ultrasonic extraction method coupled with infrared spectral characteristic analysis so as to evaluate the antioxidant capacity of total flavonoids in an important Tibetan medicine Meconopsis quintuplinervia Regel..In this study,the single factor test combined with Box-Behnken response surface method was utilized to optimize the extraction method of total flavonoids in M. quintuplinervia.Then,the difference of infrared spectra between extraction solution and solvent was analyzed.Finally,DPPH,ABTS and FRAP methods were used to determine and evaluate the antioxidant capacity of the extraction solution.The results showed that total flavonoids yield was suitable when M. quintuplinervia was extracted 58 min in 74% ethanol with liquid-to-material ratio 1∶50 (g/mL) at 64 ℃ and ultrasonic power 160 W.Under the aboved conditions,the yield of total flavonoids from M. quintuplinervia reached to 65.04±0.31 mg/g.The results of infrared spectra analysis revealed that the absorption peaks of 6 845,5 167,4 405,4 337,4 061 cm^-1 and 4 023 cm-1 in the near infrared spectra,and 3 354,2 975 and 1 647 cm^-1 in the middle infrared spectra were characteristics of flavonoids.Meanwhile,the total flavonoids inM. quintuplinervia also had good antioxidant activity.The IC₅₀ value of scavenging DPPH free radicals was 10.07 μg/mL,the antioxidant capacity measured by the ABTS method was 0.95 mmol/L,and the FRAP value was 0.94 mmol/L at the extracting concentration of 200 μg/mL.This study provides a stable and feasible extraction method and the theoretical basis for the study of infrared spectral characteristic and antioxidant capacity of total flavonoids from M. quintuplinervia.