Abstract: Black soybean which has black seed capsule is a kind of potential plant protein resource, and its protein content is up to 50%. But the protein molecule highly compressed and folded is not easy to be digested. Thus its processing and use are restricted. In this research, the 2709 proteinase was used for black soybean protein hydrolysis to produce black soybean polypeptide which had good acid-solubility and was easy to be digested and absorbed. The optimum condition of enzyme hydrolysis was determined by combining degree of hydrolysis and the ratio of acid-solubility polypeptide：substrate concentration 3.75 g/100 mL, enzyme dosage 8 000 u/g, pH 9.0, temperature 50℃, time of hydrolysis 2.0 h, degree of hydrolysis 10%, the ratio of acid-solubility polypeptide 85%. 2709 proteinase had better hydrolysis effect for black soybean protein. 1 kg black soybean was ground, hydrolyzed and separated to get rid of residue and bitterness to make 20 L black soybean polypeptide liquid which was mixed together with 80 L apple juice to make a kind of compound beverage. The product had palm-red color and special faint scent favor of natural apple juice and black soybean. Its protein and peptide content (m/V) are more than 1.5%, acidity(according to citric acid) is more than 0.4 g/100 mL.