Pile-fermentation and golden-flower fermentation are key processing steps in Tibetan dark tea, yet their effects on tea polysaccharides remain unclear. Using a 2 × 2 processing design, four polysaccharide-enriched fractions (LTPS, LFTPS, HTPS, and HFTPS) were prepared and compared. All fractions were uronic acid-rich acidic heteropolysaccharides with similar monosaccharide species but different molar ratios. Processing markedly altered molecular-weight distribution, and HFTPS showed the lowest apparent molecular weight and the highest absolute zeta potential. HFTPS also exhibited the strongest antioxidant capacity and the highest inhibitory activities against α-glucosidase, cholesterol esterase, and lipoxygenase. In a high-glucose-induced Caenorhabditis elegans model, tea polysaccharides reduced lipid accumulation, improved locomotion, prolonged lifespan, and enhanced heat- and oxidative-stress resistance. These effects were accompanied by transcriptional responses consistent with enhanced fatty acid oxidation and reduced lipogenesis. Overall, the fraction obtained after pile-fermentation followed by golden-flower fermentation showed the most favourable structural and functional profile.