Abstract: To promote the development and application of Sibiraea angustata polysaccharides (SAPs), this study optimized the cellulase-ultrasonic synergistic extraction process of SAPs using response surface methodology (RSM), and further analyzed their structural characteristics and lipid-lowering activity. The results of process optimization indicated that the order of factors influencing the yield of SAPs was: solid-to-liquid ratio > enzyme addition amount > ultrasonic time. The optimal parameters for SAPs extraction were determined as follows: liquid-to-solid ratio of 20 (v/m), enzyme addition of 3.5%, and ultrasonic time of 70 min, achieving a yield of 6.98% with extract rate of 65.23%. SAPs is an acidic heteropolysaccharide composed of 9 monosaccharide residues (Mw = 87.72 kDa), with highest galactose (32.9%), followed by rhamnose (25.7%), glucose (15%), and arabinose (12.6%). In addition, the IC₅₀ values of SAPs for scavenging DPPH and ABTS⁺· radicals were 99.53 mg/L and 94.75 mg/L respectively, indicating their potential antioxidant activity. In terms of the lipid-lowering mechanism, SAPs exhibit a positive linear dependence on bile salt binding capacity. The binding rate of bile salt exceeds 60% at 5.0 mg/mL SAPs, with the strongest binding ability observed with taurocholate. With increasing concentrations of SAPs, the levels of triglycerides (TG), total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C) in zebrafish exhibited a dose-dependent decrease. Oil Red O staining further confirmed that SAPs significantly reduced lipid droplet deposition in the zebrafish tail, with the effect demonstrating a concentration-dependent manner. The lipid-lowering effect of SAPs exhibited a significant concentration-dependent increase (P<0.05). The lipid-lowering rate reached 9.85% at 5.0 mg/mL SAPs, demonstrating that SAPs can effectively ameliorate hyperlipidemia through dose regulation. These results will lay a theoretical and technical foundation for the development of functional lipid-lowering products using SAPs.