The ultrasonic method was used for extracting flavonoids in lonicera similis hemsl and the flavonoids were determined by spectrophotometry. The recovery is 98.0%~103.0% and the coefficient of variation is less than 062%. The antioxidation effect of Lonicera Similis Hemsl was studied by flow-injection chemiluminescence. The results show that Lonicera Similis Hemsl has strong antioxidative effect.