Abstract: Crude polysaccharides from Flos. Dolichos lablab L. exhibit various biological activities, including antioxidant, hypoglycemic, and hypolipidemic effects. However, in practical applications, extreme conditions such as high-temperature infusion, gastric acid environments, and sterilization processes may compromise the stability of their biological activities. To investigate the effect of fermentation on the stability of biological activity of crude polysaccharides from Flos. Dolichos lablab L. under extreme conditions, the structural and activity changes of the polysaccharides before and after fermentation were measured using heat, acid, and sterilization treatments to evaluate the impact of fermentation on the stability of their biological activity. The results indicated that, in terms of structural characteristics, the molecular weight of crude polysaccharides from Flos. Dolichos lablab L. decreased both before and after fermentation, as well as after treatments at 100 ℃, pH=1, and 121 ℃ for 30 min. Furthermore, the molecular weight after fermentation was significantly lower than that before fermentation under all treatment conditions. In terms of biological activity, after heat, acid, and sterilization treatments, fermentation enhanced the scavenging rate of crude polysaccharides from Flos. Dolichos lablab L. against the 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonate) diammonium salt cation (ABTS⁺) radical, demonstrating excellent antioxidant stability. After heat and acid treatments, fermentation increased the α-amylase inhibition rate. However, under sterilization conditions of 121 ℃ for 20 min, fermentation did not enhance inhibition rate, whereas it improved it under all other conditions. After heat, acid, and sterilization treatments, under most conditions, the binding capacity of fermented crude polysaccharides from Flos. Dolichos lablab L. to sodium glycodeoxycholate and sodium taurodeoxycholate decreased compared to the samples before fermentation. In summary, the fermentation process enhanced the antioxidant capacity and hypoglycemic effects of crude polysaccharides from Flos. Dolichos lablab L., while improving their stability. Although no significant improvement in hypolipidemic activity was observed, the fermentation process still ensured the consistent performance of the polysaccharide in this regard. This study provides a theoretical basis for the stability of the primary biological activities of crude polysaccharides from Flos. Dolichos lablab L. during fermentation, offering practical guidance for their application in the functional food industry.