Abstract: In this study, Pleurotus eryngii being used as the material, flavonoids was extracted through ultrasonicassisted method. Response surface method was applied to obtain the optimum extracting conditions for flavonoids from Pleurotus eryngii. The effect of ethanol concentration, liquid-solid ratio, ultrasonic time and temperature on the yield of flavonoids were investigated by single factor experiments. Subsequently, the BoxBehnken center combination experimental design was used to investigate the effect of four factors on the yield of flavonoids extraction. The optimum combination was obtained by design expert 8.06 and response surface analysis. The results showed that the optimum extraction conditions were as follows:ethanol concentration80%, liquid-solid ration 1 ∶40 (g/m L) , ultrasonic temperature 80℃, ultrasonic time 100 min. Under the above optimized conditions, the yield of flavonoids was 2.92%.