Abstract: The superior preparation parameters of angiotensin converting enzyme(ACE)inhibitory peptide were studied by ultrasonic assisted enzymolysis. Defatted corn germ was pretreated under three kinds of ultrasonic equipment,and hydrolyzed by alcalase. The enzymatic hydrolysate was digested in vitro. ACE inhibitory activity of gastrointestinal digestive hydrolysate and degree of hydrolysis(DH)of corn germ in enzymatic hydrolysis process were taken as the indexes for searching for the optimal parameters of ultrasound pretreatment and enzymolysis. The results showed that the best ultrasonic working mode was 20~40 kHz dual-frequency ultrasound,power density was 120 W/L,ultrasound pretreatment time was 15 min,initial temperature of the suspension was 30℃ and substrate concentration was 50 g/L. And enzyme dosage was 3000 U/g,enzymolysis time was 30 min,pH was 9.0 and enzymolysis temperature was 50℃. Under optimal conditions,the enzymatic hydrolysates value of IC₅₀ was 4.166 mg/mL,decreased by 5.08% compared with control. The gastrointestinal digestive hydrolysate value of IC₅₀ was 3.986 mg/mL,decreased by 4.44% compared with control. The gastrointestinal digestive hydrolysate had stronger ACE inhibitory activity. The optimization technology of preparation ACE inhibitory peptide from defatted corn germ was feasible.