OBJECTIVE：To optimize ultrasonic-assisted ethanol-（NH4）2SO4 aqueous two-phase extraction technology of citru- sinol from Desmodium caudatum . METHODS ：Using the content of citrusinol as indexes ，with ethanol volume fraction ， solid-liquid ratio ，（NH4）2SO4 addition amount ，ultrasonic time and ultrasonic temperature as factors ，based on the single factor tests，Box-Behnken design-response surface methodology was used to optimize the extraction technology of citrusinol. RESULTS ： The optimized extraction technology of citrusinol included that ethanol volume fraction was 95.35％，the solid-liquid ratio was 1∶50.35 （g/mL），（NH4）2SO4 addition amount was 4.49 g，ultrasonic time was 48.7 min，ultrasonic temperature was 57.6 ℃. In 3 times of validation tests ，the extraction rates of citrusinol were 0.637 8，0.638 4，0.625 4 mg/g，respectively，which was close to predicted value（0.630 5 mg/g）. CONCLUSIONS ：The optimized ultrasonic-assisted ethanol- （NH4）2SO4 aqueous two-phase extraction technology is stable and feasible ，and can be used for the extraction of citrusinol from D. caudatum .