Abstract: Based on the ultrasonic extraction method, the optimal technological conditions for extracting flavonoids from Trifolium repens was explored. With rutin as a blank control, the total flavonoid yield rate was an inspection index, and the effect of three factors, which were ultrasonic time, ethanol concentration and liquid-solid ratio, on the extraction rate of flavonoids in Trifolium repens was studied by the sodium nitrite-aluminum-sodium hydroxide method, single-factor test and L₉（3³） orthogonal test design. The results demonstrated that the optimal extraction process conditions of total flavonoids from Trifolium repens were ultrasonic time 40 min, ethanol concentration 50%, liquid-solid ratio of 60∶1（mL∶g）. Under these conditions, the extraction rate of total flavonoids in Trifolium repens was 2.853%. The test design method was highly efficient, fast and economical. It was suitable for the research on the extraction process of total flavonoids from Trifolium repens and provided experimental basis for the effective extraction of flavonoids from Trifolium repens.

Key words: Trifolium repens, total flavonoids, orthogonal test, extraction process