Okara is a major by-product of soybean processing, which not only has negative impacts on the environment but also leads to resource waste. Soybean residue is rich in insoluble dietary fiber, which is known to have a positive effect on ulcerative colitis. This study aimed to investigate whether long-term consumption of high-purity soy isolate dietary fiber (HPSIDF) promotes the proliferation of beneficial intestinal substances, thereby alleviating intestinal damage caused by chronic ulcerative colitis (CUC). This study induced CUC using 2 % dextran sulfate sodium (DSS) and conducted a three-phase (9-week) intervention experiment. The study showed that long-term consumption of HPSIDF can regulate the level of inflammatory factors in mice and relieve damage to intestinal tissue. In addition, long-term intake of HPSIDF inhibited the degradation of Lactobacillus intestinalis and promoted the proliferation of Oscillospira and the production of beneficial substances such as Agmatine and Betaine, which played an important role in the maintenance of intestinal bacterial flora and the improvement of the internal environment. This study clarified that long-term intake of HPSIDF not only changes the intestinal self-properties but also promotes the proliferation of beneficial flora and metabolites, providing a solution strategy for the high-value utilization of okara.