Abstract: An ultra-high performance liquid chromatography method for the determination of 8 constituents in Qingzao Jiufei Decoction was established and the basis of related chemical substances with antioxidant activity in Qingzao Jiufei Decoction was explored. The separation was performed on a Waters Cortecs RP Shield C18 (150 mm×2.1 mm, 1.6 μm) using UHPLC-DAD as the mobile phase was water (containing 0.1% phosphoric acid)-acetonitrile with flow rate of 0.30 mL·min^-1 by gradient elution ① determining 5 constituents (amygdalin, liquiritin, liquiritin apioside, rutin and isoquercitrin) at the wavelength of 210 nm, 237 nm and 358 nm. Under gradient elution ②, 3 constituents (glycyrrhizin, glycyrrhizic acid and sesamin) were determined at the wavelength of 210 nm and 265 nm. The IC₅₀ of 10 batches of Qingzao Jiufei Decoction scavenging 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS⁺) free radicals obtained through test and Probit model was analyzed for correlation with the contents of 8 constituents. The established methods had a good linear relationship (r>0.999), good repeatability and stability. The recovery rate was between 82.8% and 112.4%. In a series of concentration range, the higher the concentration of Qingzao Jiufei Decoction, the stronger the free radical scavenging effect. There was a significant correlation between the content of rutin and glycyrrhizic acid and the IC₅₀ of scavenging free radicals. The content determination methods established in this experiment provide a basis for a reasonable and scientific evaluation of the quality of Qingzao Jiufei Decoction. Qingzao Jiufei Decoction has antioxidant activity, which is significantly positively correlated with the content of rutin and glycyrrhizic acid.