[Objective] The research aimed to optimize the extraction technology of total flavonoids from Folium Menthae haplocalycis and study its antioxidant activity, and to provide a basis for extraction and utilization of total flavonoids from FOLIUM MENTHAE HAPLOCALYCIS. [Method] Taking the extraction rate of total flavonoids as index, L9(34) orthogonal test with four factors and three levels was used to optimize the extraction process of total flavonoids from FOLIUM MENTHAE HAPLOCALYCIS by ultrasound-assisted extraction method. The ·OH scavenging activities of water and ethanol extracts from FOLIUM MENTHAE HAPLOCALYCIS were further studied. [Result] The results showed that the optimal extraction technology of total flavonoids from Folium Menthae haplocalycis was as follows: volume fraction of ethanol 40%, solid-liquid ratio 1∶30, ultrasonic power 400 W, extraction temperature 50 ℃, and extraction time 40 min. Under this condition, the extraction rate of total flavonoids was 6.58%. The water extracts from FOLIUM MENTHAE HAPLOCALYCIS had a good scavenging effect on ·OH, and its ·OH scavenging rate was gradually increased with the raising total flavonoids content. The maximum scavenging rate of water extracts was 44.23%. The scavenging effect of ethanol extracts on ·OH was increased slowly first, then decreased quickly and continuously with the increasing of total flavonoids content, but less than the effect of its water extracts in whole. [Conclusion] The method of extracting total flavonoids by using ethanol as the solvent assisted with ultrasonic wave was simple, and had strong maneuverability. The total flavonoids from FOLIUM MENTHAE HAPLOCALYCIS had strong scavenging effect on ·OH, and can be developed and utilized. [Objective] The research aimed to optimize the extraction technology of total flavonoids from Folium Menthae haplocalycis and study its antioxidant activity, and to provide a basis for extraction and utilization of total flavonoids from FOLIUM MENTHAE HAPLOCALYCIS. [Method] Taking the extraction rate of total flavonoids as index, L9 (34) orthogonal test with four factors and three levels was used to optimize the extraction process of total flavonoids from FOLIUM MENTHAE HAPLOCALYCIS by ultrasound-assisted extraction method. The · OH scavenging activities of water and ethanol extracts from FOLIUM MENTHAE HAPLOCALYCIS was further studied. [Result] The results showed that the optimal extraction technology of total flavonoids from Folium Menthae haplocalycis was followed: volume fraction of ethanol 40%, solid-liquid ratio 1:30, ultrasonic power 400 W, extraction temperature 50 ℃, and extraction time 40 min. Under this condition, the extraction rate of total flavonoids was 6.58% water extracts from FOLIUM MENTHAE HAPLOCALYCIS had a good scavenging effect on · OH, and its · OH scavenging rate was gradually increased with the raising total flavonoids content. The maximum scavenging rate of water extracts was 44.23%. The scavenging effect of ethanol extracts on · OH was increased first, then decreased quickly and continuously with the increasing of total flavonoids content, but less than the effect of its water extracts in whole. [Conclusion] The method of extracting total flavonoids by using ethanol as the solvent assisted with ultrasonic wave was simple, and had strong maneuverability. The total flavonoids from FOLIUM MENTHAE HAPLOCALYCIS had strong scavenging effect on · OH, and can developed and utilized.