Abstract: Objective:To optimize the ultrasonic-microwave synergistic extraction process of flavonoids from Eichhornia crassipes by Box-Behnken design,and to analyze antioxidant activity from different parts. Methods:Ultrasonic power,microwave power,material-to-liquid ratios and extraction time were set as the main influencing factors,based on the single factor experiment,the total flavonoid yield was took as the response value,response surface methodology (RSM) was used to optimize the extraction process of total flavonoids from Eichhornia crassipes. By the research of the total reduction ability,DPPH and superoxide anion free radical scavenging abilities to analysis the antioxidant ability of different parts from Eichhornia crassipes. Results:The optimal extraction conditions were determined as follows:Ultrasonic power 600 W,microwave power 400 W,material-to-liquid ratios 1:22 (g/mL),extracting time 21 min. Under these conditions,the yield of flavonoids was 3.64%±0.07%. The predicted value of the regression model was similar to the real value,and the model fits well. The antioxidant activity of flavonoids in different parts was:Leaf > root > stem,the IC₅₀ of scavenging DPPH and superoxide anion free radical respectively were:the leaf of Eichhornia crassipes 0.569,0.389 mg/mL,the root of Eichhornia crassipes 0.754,0.555 mg/mL,the stem of Eichhornia crassipes 0.837,0.646 mg/mL. Conclusion:The process conditions of ultrasonic-microwave synergistic extraction of flavonoids from Eichhornia crassipes by response surface methodology optimization were reasonable and had high efficiency. The obtained flavonoid had good antioxidant capacity and could be further developed and utilized.