［Objective ］ This study aimed to achieve high yield and green extraction of flavonoids from Goji (Lycium barbarum L.) leaves using ultrasonic assisted aqueous two -phase method,and to evaluate the activity of extract.［Methods ］ Single factor and PB (Plackett -Burman ) experiments were conducted to investigate the influence of various factors on the extraction efficiency of flavonoids.Three parameters were chosen to optimize the extraction conditions using a Central Composite Design (CCD ) of the response surface experiment:the amount of polyethylene glycol (PEG 400),the amount of ammonium sulfate,and the solid -liquid ratio.The extract's activity was assessed using an activity inhibition test of pancreatic lipase.［Results］ The optimal process conditions for ultrasonic -assisted aqueous two -phase extraction of flavonoids from Goji berry leaves were:28% polyethylene glycol 400,16% ammonium sulfate,ultrasonic power of 250 W,ultrasonic treatment time of 40 minutes,ultrasonic treatment temperature of 40 ℃,and solid -solid ratio of 1∶30 (g/g).Under these conditions,the total flavonoid content of the extract was (486.30±3.29) mg/g,which had a significant inhibitory effect on pancreatic lipase activity,and the half inhibition concentration (IC50) was 1.06 mg/mL.［Conclusion ］ Under the optimal extraction conditions,the flavonoids extracted from L.barbarum leaves by ultrasonic -assisted aqueous phase method had high yield and low solvent residue,and the flavonoids from L.barbarum leaves obtained by this method had a good inhibitory effect on pancreatic lipase.