Abstract: In order to study the effects of different working mode of ultrasound on the degree of enzymatic hydrolysis and ACE inhibitory activity of defatted wheat germ,five kinds of working mode of ultrasound,energy aggregation counter flow single- frequency ultrasound,energy aggregation counter flow dual- frequency ultrasound,pulsed and sweeping frequency ultrasound,divergence triple- frequency ultrasound and opposite- site dual- frequency ultrasound were used to pretreat of defatted wheat germ under the same condition in this article.The one- factorial experiments were taken to search the best pretreatment parameters of ultrasound.The results illustrated that ultrasound pretreatment had no significant effect on the degree of hydrolysis but could increase the ACE inhibitory activity of enzyme products significantly.The best ultrasonic working mode was 40 k Hz /28 k Hz pulse plate dual- frequency ultrasound. With this working mode,the enzymatic hydrolysates value of IC₅₀ could drop to2.483 mg / m L under the following optimal ultrasound pretreatment conditions: ultrasonic power per unit volume of60 W/ L,ultrasound time of 70 min,ultrasonic initial temperature at 60 ℃,the substrate concentration 7%.As a better result,the value of IC₅₀ decreased by 5.8% compared with control group.