The work aims to prepare dietary fibers with rice bran to increase the utility ratio of dietary fibers in rice bran by extrusion. With defatted rice bran powder as raw material and the content of soluble dietary fiber as indicator, extrusion experiments were performed to study the effect of different extrusion temperatures, water contents of the raw materials and screw speeds on the experiment result. The microstructure, functional group and grain size change of dietary fiber in rice bran before and after extrusion were analyzed through SEM, FTIR and LPSA. The optimal parameter conditions for rice bran dietary fiber extrusion were obtained, which were water content of raw material 22%, extrusion temperature 130 ℃ and screw speed 100 r/min. On this basis, it was measured that the optimal yield of soluble dietary fiber in race bran was 23.63%. The microstructure of extruded rice bran dietary fiber had honeycomb structure. The infrared spectrum showed that the absorption peak of sugar in extruded rice bran dietary fiber changed significantly, and the particle size distribution also changed. The application of the response surface methodology verifies the optimal extrusion parameters of race bran and improves the content of soluble dietary fiber in race bran. The function of dietary fiber in race bran also changes with the structural change.