Polysaccharides are the major bioactive composition of Polygonatum sibiricum (P. sibiricum). However, the structural and functional identifications of these polysaccharides were still limited. Herein, we isolated a novel P. sibiricum polysaccharides (PSPF) and explored its potential function and mechanism in alleviating hyperlipidemia. PSPF were purified by diethylaminoethyl-sepharose fast flow (DEAE-Sepharose FF) and cross-linked dextran gel LH-20 (Sephadex LH-20) column chromatography, and identified by gel-permeation chromatography, methylation analysis, fourier transform infrared spectrometer (FT-IR), nuclear magnetic resonance (NMR), and gas chromatography-mass spectrometry (GC-MS). Their molecular weight (Mw), polysaccharide composition, and chemical structure were characterized. Furthermore, egg yolk emulsion-induced acute hyperlipidemia mouse model was constructed to evaluate the lipid-lowering efficacy and the underlying mechanism of PSPF. It was found that PSPF, with the Mw of 3592 Da, were prepared and mainly consisted of fructan with →1)-β-D-Fruf-(2 → main chain and →6)-β-D-Fruf-(2 → side chains. In addition, PSPF supplements efficiently reduced liver lipid accumulation, alleviated hepatocyte steatosis, and upregulated the AMP-activated protein kinase (AMPK) pathway, thereby enhancing fatty acid oxidation and decomposition. These results indicate that PSPF may serve as the potential dietary supplements for lipid reduction.