Abstract: To preliminarily assess the primary reasons for the reduction in polysaccharide content in Polygonatum sibiricum processed through the "Nine Steaming-Nine Processing" method and its impact on the in vitro activity of Polygonatum sibiricum polysaccharides, this study measured the levels of 5-hydroxymethylfurfural (5-HMF) and advanced glycation end-products (AGEs) in Polygonatum sibiricum processed through the "Nine Steaming-Nine Processing" method. The study also examined the structural changes of purified polysaccharides from Polygonatum sibiricum before and after the "Nine Steaming-Nine Processing" process and analyzed the influence of these changes on the in vitro activity of Polygonatum sibiricum. The results indicated that the "Nine Steaming-Nine Processing" induced the Maillard reaction in Polygonatum sibiricum, resulting in a 5-HMF content of (631.3±21.5) μg/g, and the levels of carboxymethyl lysine (CML) and carboxyethyl lysine (CEL) were (342.4±11.3) μg/g and (63.7±9.8) μg/g, respectively. This processing also had varying degrees of impact on the structure and composition of Polygonatum sibiricum polysaccharides. The glucose (Glc) content increased, while mannose (Man) and galacturonic acid (GalUA) content significantly decreased, with Man decreasing from 34.53% to 17.06%, and GalUA decreasing from 9.59% to 1.77%. The research suggests that Polygonatum sibiricum undergoes the Maillard reaction during the "Nine Steaming-Nine Processing", leading to the formation of a certain amount of AGEs. Simultaneously, the "Nine Steaming-Nine Processing" method can enhance the in vitro hypoglycemic activity of Polygonatum sibiricum polysaccharides to a certain extent.