Abstract: To study the preparation of garlic antihypertensive peptide by enzymatic hydrolysis and its ultrafiltration separation systematically. After enzymatic hydrolysis,polypeptide components of different molecular weight ranges were obtained by membrane filtration,and the activity of each component was evaluated by ACE inhibitory activity. The main research results were as follows:the effect of alkaline protease treatment was better,and the ACE inhibition rate was relatively higher when the hydrolysis time was 1 h. The best enzymatic hydrolysis conditions were temperature 50℃,pH11,substrate concentration 45 g/L,enzyme bottom ratio 3%,with the ACE inhibition rate of 83.91%±0.13%,and the IC₅₀ was(157.87±0.44) μg/mL. It was found that the inhibitory activity of some peptides with molecular weight below 3 kDa was significantly higher than that of other molecular weight ranges(P<0.05). The optimized ultrafiltration process was:operating pressure 0.25 MPa,temperature 25℃,solution concentration 4%,at this time the membrane flux was(7.32±0.19) L/(m²·h),IC₅₀ was(63.27±0.25) μg/mL. The amino acid compositions of this fraction showed acidic amino acid,hydrophobic amino acid,Asp,and Glu were abundant,and their contents were 35.78,32.86,21.66 and 14.12 mg/100 mL,respectively. The molecular weight distribution results indicated that the percent of 2000~2500 Da part was up to 49.50%. The research provided a reference for the deep development and utilization of garlic protein,which had certain theoretical level and practical application value.