Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract, often associated with dysregulated immune responses, gut barrier dysfunction, and microbial imbalance. In this study, a novel polysaccharide from Polygonatum kingianum (PKP) was extracted and structurally characterized as a mixed-type fructan. Using a dextran sulfate sodium (DSS)-induced colitis mouse model, we demonstrated that PKP treatment significantly alleviated clinical symptoms of colitis, including body weight loss, colon shortening, and histological damage. PKP enhanced tight junction protein expression of zonula occludens-1 (ZO-1) and occludin, reduced the levels of pro-inflammatory cytokine interleukin-6 (IL-6), limited neutrophil and macrophage infiltration in colon tissue. Furthermore, PKP restored intestinal microbiota diversity by increasing the abundance of Firmicutes and reducing the abundance of Verrucomicrobiota. Metabolomics analysis revealed that PKP modulated gut metabolites, notably increasing levels of myristic acid and desmosterol, both associated with anti-inflammatory effects. Collectively, these findings suggest that PKP exerts protective effects against colitis by reinforcing intestinal barrier integrity, modulating immune responses, and regulating gut microbiota and metabolic homeostasis.