Abstract: In this study, the wheat bran dietary fiber was fermented by Basidiomycota, Candida utilis and Lactobacillus plantarum in solid-state, in order to reduce the content of insoluble dietary fiber in wheat bran dietary fiber and improve its nutritional value and food processing characteristics. Meanwhile, the basic composition and micro-morphology of wheat bran dietary fiber between before and after fermentation were analyzed. In this study, four variables including inoculation amount, liquid-solid ratio, fermentation duration, and fermentation temperature were chosen for single-factor and response surface design experiments. The optimized conditions for solid-state fermentation of mixed strains were determined as follows:inoculation amount 15.1%, liquid-solid ratio 1.7:1 mL/g, fermentation duration 11 d and fermentation temperature 28℃. Furthermore, the physical and chemical properties of the fermented wheat bran dietary fiber were measured and analyzed. The results showed that the degradation rate of insoluble dietary fiber under this process condition was 19.194%, and the content of insoluble dietary fiber was effectively reduced and the physical structure of wheat bran dietary fiber was altered. In addition, the content of soluble dietary fiber was increased from 3.91% to 7.47% compared to that before optimization. The protein content also rose from 4.06% pre-fermentation to 9.08% after modification, thereby improving the nutritional attributes of the wheat bran dietary fiber. The water-holding capacity and oil-holding capacity of wheat bran dietary fiber were enhanced by 1.48 times and 1.42 times, respectively, after optimization. The high oil-holding capacity and excellent water-holding capacity contributed to strong holding power of the products and facilitated the formation of gels and stable structure. The surface structure of fermented wheat bran dietary fiber became more porous, presenting a large amount of fragmented structure, and the surface of the dietary fiber was damaged. Therefore, mixed bacterial fermentation method can effectively increase the degradation rate of insoluble dietary fiber, as well as enhance its nutritional value and food processing characteristics. These results provided a technical support for extensive use of wheat bran dietary fiber as a food additive.