The concept of food and medicine homology (FMH), which emphasizes the dual role of natural compounds in both medicinal and nutritional contexts, has seen significant development and presents promising application prospects in various fields. Polysaccharides, as the representative bioactive macromolecules in FMH resources, have demonstrated a wide range of biological activities in vitro and in vivo, encompassing antioxidant, anti-tumor, anti-aging, immunomodulatory, and metabolic regulatory effects. However, their inherent structural complexity and functional heterogeneity pose significant challenges to their rapid and accurate detection. Traditional analytical methods often lack the requisite sensitivity, specificity, or real-time capability essential for the integrated analysis of functional components. Emerging biosensing technologies, renowned for their high sensitivity and specificity, are revolutionizing the detection of FMH plant polysaccharides (FMHPPs) by correlating structural characteristics with their functional properties. This review comprehensively summarizes recent advances in the extraction, structural characterization, and bioactivities of FMHPPs, with a particular focus on the application and future perspectives of novel biosensing technologies for their detection and functional assessment, aiming to foster their development in functional foods, pharmaceuticals, and related industries.