Abstract: Taking daylily (Hemerocallis L.) leaf substitute tea as the raw material, the extraction process of polyphenols was optimized by ultrasonic-assisted extraction combined with response surface methodology, and the types of polyphenols and their antioxidant activity were determined simultaneously. With gallic acid as the reference, liquid chromatography-mass spectrometry was used to identify the types of polyphenols, and ultraviolet-visible spectrophotometry was employed to determine the content of polyphenols. Taking ethanol concentration, ultrasonic time, ultrasonic power, and solid-liquid ratio as influencing factors, orthogonal experiment was adopted to analyze the interaction among the four factors, and the optimal extraction conditions of total phenols were determined and verified. The antioxidant activity was evaluated by determining the scavenging capacities of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals and 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The results showed that when the ethanol volume fraction was 59.78%, the liquid-to-solid ratio was 40∶1 (mL/g), the extraction time was 51.56 min, and the ultrasonic temperature was 49.98 ℃, the extraction rate of polyphenols could reach 2.65%; moreover, with the increase of polyphenol concentration, the scavenging rates of DPPH radicals and ABTS⁺ increased significantly, confirming that the polyphenols in daylily leaf substitute tea had good antioxidant activity.