Non-starch polysaccharides have been demonstrated to have significant benefits in treating some chronic metabolic diseases such as hyperglycemia. However, the preventive effect of non-starch polysaccharides from Castanea mollissima Bl. (CMNSP) on type 2 diabetes mellitus (T2DM) remain underexplored. The objective of this study was to investigate the effect of CMNSP on glucose and lipid metabolism, intestinal barrier, gut microbiota and their metabolites in high fat diet/streptozotocin-induced T2DM mice. The results revealed that CMNSP significantly mitigated hyperglycemia, insulin resistance, hyperlipidemia, and prevented pancreatic atrophy, hepatic steatosis and enhanced the expression at mRNA level and corresponding protein of PI3K/AKT/Glut2 signaling pathway in liver. Moreover, CMNSP enhanced the level of SCFAs and restored intestinal barrier damage and gut microbiota disturbance in diabetic mice. Further fecal metabolomics analysis identified that CMNSP primarily influenced the metabolic pathways such as Primary bile acid biosynthesis and Taurine and hypotaurine metabolism, and were significantly correlated with changes in dominant bacterial genera including Bacteroides and Lactobacillus.