Tremella fuciformis polysaccharides have rich bioactivities, while low molecular weight polysaccharides have higher bioavailability and nutritional value. In this study, it was investigated that the structural characteristics of low molecular weight polysaccharides from Tremella fuciformis (TFLP) prepared by acid hydrolysis method, its impact on antioxidant capacity and stress resistance of Caenorhabditis elegans, and potential mechanisms. TFLP was an acidic polysaccharide mainly composed of mannose and xylose with a molecular weight of 106 kDa. TFLP could prolong the median lifespan of C. elegans under heat stress and acute oxidative stress conditions through significantly reducing the malondialdehyde (MDA) level and increasing the activity of antioxidant enzymes total-superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px) and catalase (CAT). The intervention of high-dose TFLP significantly prolonged the median lifespan of C. elegans under heat stress and acute oxidative stress conditions by 24.47% and 7.84%, respectively. At the same time, the MDA level significantly decreased by 69.59%, and the levels of T-SOD, GSH-Px and CAT increased significantly by 2.22, 1.28 and 0.53 times, respectively. Meanwhile, the transcription levels of daf-16, fat-5, fat-7, and hsf-1 mRNA in C. elegans treated with TFLP were significantly increased, while the transcription levels of akt-1 and daf-2 mRNA were significantly reduced. In addition, propanoate metabolism, valine, leucine and isoleucine degradation metabolism and vitamin B6 metabolism were key metabolic pathways for TFLP to enhance antioxidant capacity and stress resistance in C. elegans. These results indicated that TFLP could enhance in vivo antioxidant capacity and stress resistance by improving the levels mRNA transcription and metabolites, and it provided new evidence for TFLP to exert in vivo antioxidant activity.