Utilizing Cyperus esculentus meal as raw material， soluble dietary fiber (SDF) was extracted from it using a composite enzyme method (α-amylase， glucoamylase and trypsin). The SDF was enzymatically modified by cellulase， and the enzymatic hydrolysis conditions of cellulase (enzyme addition amount， enzymatic hydrolysis temperature， enzymatic hydrolysis time， enzymatic hydrolysis pH value) were optimized. The content， physicochemical properties， structural characteristics and antioxidant capacity of SDF before and after modification were compared. The results showed that the optimum conditions for cellulase modification were as follows: pH 6.5， hydrolysis temperature 40 ℃， enzyme addition 0.9%， hydrolysis time 2.5 h， SDF content increased from 3.55% to 10.86%. By observing the ultrastructure， it was found that the modification changed the fiber structure， weakened the diffraction peak intensity， improved its structural characteristics， and improved the microstructure characteristics. In addition， cellulase modification increased the water holding capacity， swelling capacity and oil holding capacity of Cyperus esculentus meal SDF by 54.58%， 43.73% and 38.40%， respectively. When the mass concentration of SDF was in the range of 0.5-5 mg/mL， the scavenging ability of modified SDF on 1，1-diphenylpicrylhydrazyl (DPPH) radical， 2，2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical， hydroxyl radical (·OH) was significantly improved. The highest values were 42.87%， 44.05% and 41.46%， and the ability to reduce Fe3+ increased by 1.25 times at 5 mg/mL. This study provides a reference for further improving the development value of Cyperus esculentus meal and its application in human food and pharmaceutical industry.