Abstract Background In recent years, the biological activities of polysaccharides derived from Chinese herbal medicones have garnered increasing attention. Polygonatum cyrtonema Hua, a widely used traditional Chinese medicinal herb, possesses significant healthcare value. However, the structure–activity relationship between polysaccharide structures and biological functions remains to be fully elucidated. Methods Crude Polygonatum cyrtonema Hua polysaccharides (PCHP) were extracted using hot water extraction followed by alcohol precipitation. The extract was subsequently purified through DEAE seplife FF chromatography, yielding two franctions: PCHP-1 and PCHP-2. Because of the highest content and the better solubility, PCHP-1 was further purified using Sephacryl S-400HR column chromatography to obtain a purified fraction designated as PCHP-1A. Subsequently, The structural characteristics of PCHP-1A were comprehensively analyzed through monosaccharide composition analysis, scanning electron microscopy (SEM), Fourier transform-infrared spectroscopy (FT-IR), methylation analysis, and nuclear magnetic resonance (NMR) spectroscopy. Additionally, the antioxidant and hypoglycemic activities of PCHP-1A were evaluated though in vitro experiments. Results Structural analysis revealed that PCHP-1A, with an average molecular weight of 2.90 × 104 Da, is comprised of fructose (Fru), glucose (Glc), galactose (Gal), mannose (Man), arabinose (Ara) and rhamnose (Rha). PCHP-1A exhibited a compact and curly spherical molecule conformation, and SEM analysis revealed its smooth, porous, clastic or lamellar microstructure. Comprehensive FT-IR, GC–MS, and 1D/2D NMR analyses indicated that the main chain of PCHP-1A consists of → 1)-β-d-Fruf-(2 → , → 1,6)-β-d-Fruf-(2 → , and → 6)-α-d-Glcp, with branch chains primarily composed of β-d-Fruf-(2 → linked at the O-6 position of → 1,6)-β-d-Fruf-(2 →. Biological activity assays demonstrated that at a concentration of 4.0 mg/mL, PCHP-1A exhibited a DPPH scavenging rate of 56.92 ± 1.42% and an inhibitory capacity against ·OH radicals of 23.27 ± 1.80 U/mL. Furthermore, PCHP-1A showed significant hypoglycemic activity, with an IC50 value of 5.15 ± 1.09 mg/mL. Conclusions This study successfully isolated and purified polysaccharide from Polygonatum cyrtonema Hua, elucidated its fundamental structure, and investigated its antioxidant and hypoglycemic activities. The findings provide a theoretical foundation for understanding the structure–activity relationship of the polysaccharide and suggest that Polygonatum cyrtonema Hua polysaccharide may be a natural potential antioxidant and hypoglycemic agent. Graphical Abstract