Soluble dietary fiber was obtained from insoluble dietary fiber of soybean residue which was alkali hydrolyzed by treatment with cellulase.Based on the single-factor experiment and the response surface experiment,the relationships between the yield of soluble dietary fiber and enzymolysis factors were studied.Results showed that the effect of four factors on the yield of soluble dietary fiber orderly from high to low was as follows: enzyme dossage,enzymolysis time,enzymolysis temperature,and pH.The optimum enzymolysis conditions were as follows: enzyme dossage 1.80%,enzymolysis time 3.5 h,enzymolysis temperature 48℃,pH 4.8.Under these conditions,the yield of soluble dietary fiber could reach 7.64%,and the quality of soluble dietary fiber was consistent with the quality of the country's grain industry standards.Results from scanning electron microscopy showed that the particle of soluble dietary fiber was smaller and honeycomb which was beneficial to the improvement of its hydration.