An ultrasound-assisted extraction technique was used to extract the total flavonoids from QingLi Cao. The optimal conditions were ethanol concentration 59.20%, liquid-to-solid ratio 31.15 mL/g, extraction time 57.42 min and extraction temperature 58.57°C, which were determined using response surface methodology. The antioxidant activities including reducing power, ABTS+, DPPH, superoxide anion and hydroxyl radical were evaluated, which suggested significant antioxidant activities.