Abstract: Objective:To study the double enzyme compound enzyme preparation of soybean protein isolated soy peptide segments of the relative molecular weight distribution and activity of antihypertensive effect of experimental hypertensive rats. Methods:Through the optimization of single factor experiment, orthogonal experiment was used to optimize the compound enzyme process, the enzyme solution of angiotensin converting enzyme(ACE)inhibitory rate was as the index to optimize the process by ultrafiltration and nanofiltration, the best molecular fragments left nitro arginine(L-NNA)induced hypertension model rats were given different doses of the active fragment of test. Results:The optimum conditions of double enzyme solution was:the ratio of material to liquid 1:20 g/mL, enzymolysis temperature of 50℃, the ratio of enzyme to substrate 3%, enzymatic hydrolysis under the conditions of pH7.0 by bromelain hydrolysis for 2 h, then adding 4% trypsin enzyme substrate ratio, control the temperature of 40℃ and the enzyme pH was 8.0 under the condition of enzymatic hydrolysis for 4 h, the hydrolysis degree was 35.31% to ACE soybean peptides. After HPLC enzyme molecular weight distribution of the hydrolysates of soybean protein, polypeptide and protein solution containing the separation of the relative molecular mass was mainly in the range of 5000~1.0×10⁵ Da in double enzyme solution, the relative molecular mass of the main range of protein and peptide hydrolysates were obtained by ultrafiltration in 500~4000 Da, the best active fragment was 1000~3000 Da, pharmacological experiments showed that, compared with the model control group each group had lower blood pressure, and the soybean peptide dose group had significant difference(p<0.05), when the soybean peptide in high dose group and captopril group. Conclusion:The relative molecular weight of soybean peptides prepared by double enzyme complex hydrolysis is smaller, and the active fraction has a significant hypotensive effect on hypertensive rats.