Abstract: The study investigated the effect of countercurrent ultrasound pretreatment of rice protein on the preparation of ACE peptides by enzymatic hydrolysis of alkaline proteases. First,the rice protein was extracted from the rice residue. With the ACE inhibition rate as the main index and the degree of hydrolysis as the auxiliary index,the single factor stepwise optimization method was used to optimize the substrate concentration,time,temperature and pH of the enzymatic reaction. On this basis,the optimal ultrasonic parameters of the countercurrent ultrasound mode were screened out. The results showed that the optimum conditions were as follows:substrate concentration was 30 g/L,enzyme dosage(E/S)was 7.5%,temperature was 50 ℃,pH was 8.5 and enzymolysis time was 60 min,under this conditions,the ACE inhibition rate was 45.59% and the degree of hydrolysis was 21.49%. The optimal ultrasonic parameters were as follows:ultrasonic frequency was 20 kHz,power density was 170 W/L,time was 12.5 min. Under this conditions,the inhibition rate of ACE was 72.24% and the degree of hydrolysis was 21.64%. Compared with the untreat group,the ACE inhibition rate increased by 57.42%. Compared with the traditional ultrasound group,ACE inhibition rate increased by 11.36%. The results showed that the countercurrent ultrasonic assisted enzymatic hydrolysis method could effectively improve the enzymolysis efficiency,reduce the energy consumption and promote the preparation of ACE inhibitory peptide.