Abstract: In order to increase the utilization value of Lavandula angustifolia (LA) residue and provide a theoretical basis for the development and utilization of LA waste, the extraction process of total triterpenoids from LA was optimized and its antioxidant activity was determined in vitro. Taking the yield of total triterpenes in LA as the evaluation index, the single factor experiments and the response surface methodology were used to optimize the extraction process of ultrasonic-assisted extraction of total triterpenes from LA. The results showed that the optimum extraction conditions were ethanol concentration 89%, ratio of material to liquid 1:33 (g/mL), extraction time 60 min, and ultrasonic power 70% (445 W). The theoretical extraction volume was 39.64 mg/g, and the actual one was (39.95±0.32) mg/g under this optimum condition, which was close to the predicted value. Afterwards, using V_C as a control, DPPH free radical, OH free radical, and O₂⁻ free radical scavenging experiments were subjected to measure the anti-oxidant activity of total triterpenes, and their scavenging rates were 86.83%, 42.06% and 47.93%, respectively. After the optimization of the ultrasonic-assisted extraction process conditions, the total triterpenes extracted from LA is significantly increased, and the extract has strong antioxidant activity, which provides a theoretical basis for the reuse of LA waste to further tap the potential value.