Abstract: In order to study the extraction process and antioxidant properties of flavonoid in Fagopyrum esculentum Moench leaves. The ultrasonic-assisted extraction process of flavonoids from Fagopyrum esculentum Moench leaves was optimized by response surface method, the contents of flavonoids was analyzed by high performance liquid chromatography (HPLC), and the antioxidant activity was explored.The results showed that when the ultrasonic frequency was 45 kHz, the ultrasonic power was 100 W, the liquid -solid ratio was 30:1(mL:g), the ultrasonic time was 22 min, the ultrasonic temperature was 28 ℃, and the volume fraction of ethanol was 51%, the yield of flavonoids in Fagopyrum esculentum Moench leaves was 80.311mg/g. The relative error was 1.35% compared with the predicted value of 81.414 mg/g, which proved that the theoretical predicted value of the model well fitted with the actual value. The result of HPLC showed that rutin and quercetin were the main components of flavonoid in Fagopyrum esculentum Moench leaves, and their contents were 66.5% and 13.9%, respectively. The antioxidant activity test showed that the half maximal inhibitory concentration (IC₅₀) of the flavonoids to DPPH·, ABTS⁺· and ·OH was 0.012, 0.044, 0.344 mg/mL, respectively, indicated that the flavonoids had strong antioxidant capacity. This experiment provided a theoretical basis for the comprehensive utilization of Fagopyrum esculentum Moench leaves.