Background: Polygonatum sibiricum polysaccharide (PSP) can improve insulin resistance and inhibit oxidative stress. However, the detailed anti-diabetic mechanism of PSP is still poorly defined. Methods: In this study, the anti-diabetic, anti-inflammatory and anti-oxidative effects of PSP were evaluated on a type 2 diabetes mellitus (T2DM) rat model. Furthermore, we investigated the changes in gut microbiota and serum metabolites in T2DM rats after PSP treatment through 16S rRNA sequencing and untargeted metabolomics analyses. Results: Our results showed that PSP exhibited significant anti-diabetic, anti-inflammatory and anti-oxidative effects on T2DM model rats. In addition, 16S rRNA sequencing showed that PSP treatment decreased the Firmicutes/Bacteroidetes ratio in the gut. At the genus level, PSP treatment increased the relative abundances of Blautia, Adlercreutzia, Akkermansia and Parabacteroides while decreasing Prevotella, Megamonas funiformis and Escherichia. Untargeted metabolomics analysis revealed that PSP treatment could affect 20 metabolites, including hexanoylglycine, (+/-)5(6)-DiHET, ecgonine, L-cysteine-S-sulfate, epitestosterone, (+/-)12(13)-DiHOME, glutathione, L-ornithine, D-mannose 6-phosphate, L-fucose, L-tryptophan, L-kynurenine, serotonin, melatonin, 3-hydroxyanthranilic acid, xylitol, UDP-D-glucuronate, hydroxyproline, 4-guanidinobutyric acid, D-proline in T2DM model rats, these metabolites are associated with arginine and proline metabolism, tryptophan metabolism, amino sugar and nucleotide sugar metabolism, pentose and glucuronate interconversions, glutathione metabolism, arginine biosynthesis, ascorbate and aldarate metabolism pathways. Spearman correlation analysis results showed that the modulatory effects of PSP on the arginine and proline metabolism, tryptophan metabolism, and glutathione metabolism pathways were related to the regulation of Prevotella, Megamonas funiformis, Escherichia, Blautia and Adlercreutzia. Conclusion: Our research revealed the therapeutic, anti-inflammatory and anti-oxidative effects of PSP on T2DM. The mechanisms of PSP on T2DM are associated with improving the dysbiosis of gut microbiota and regulating arginine and proline metabolism, tryptophan metabolism, and glutathione metabolism in serum.