Abstract: In this paper,taking Phaseolus Vulgaris as row material,alkaline protease hydrolysis was used to prepare coloured kidney bean polypeptide.Enzymolysis conditions such as enzymolysis temperature,enzymolysis time,p H value and enzyme dosage were optimized by means of designing orthogonal experiments.The results showed that the optimum conditions were as follows: temperature 60 ℃,enzymolysis time 4 h,p H7.5,enzyme dosage 2000 U /g. Under this condition,the concentration of polypeptides in Phaseolus Vulgaris was 0.954 mg / m L. This paper proposes a method for extracting polypeptides from Phaseolus Vulgaris,and aims to lay a foundation for further exploration and utilization of polypeptides from Phaseolus Vulgaris in future.