In the extraction of flavonoids from Opium graveolens L.with supercritical CO2,four operating parameters such as extractive pressure,temperature,time and cosolvent dosage that affect extraction yield of flavonoids were investigated.Box-Behnken response surface methodology design was applied to establish a regression model describing the relationship between the extraction efficiency and four operating parameters.The results showed that supercritical CO2 extraction process were impacted significantly by extracting pressure,temperature and extracting time.The optimum extraction conditions were: extraction temperature 70℃,extraction pressure 30 MPa,extraction time 2.5 h and dosage of alcohol 1 mL/g.Under these conditions,the average yield of flavonoids in three replicated experiments could reach 9.03%.which was very close to the predicted.