The alcalase was selected for hydrolysis of silver carp protein, ultrafitration(UF) cup was used as a controllable reactor to enzymatic hydrolysis, and effects of membrane type and operation pressure on the nitrogen yield,degree of hydrolysis, average length of peptide chain, molecular weight distribution were studied. Results showed that ultrafiltrating at operational pressure 0.15 MPa with 10 k D membrane at the optimum enzymatic conditions, the average length of peptide chain, degree of hydrolysis and nitrogen yield of the permeate were 3....