Abstract: In this study, choline chloride/lactic acid/guaiacol ternary deep eutectic solvent (DES) was used to extract Ganoderma lucidum polysaccharides (GLPs). The operational parameters of GLPs extraction by DES were optimized, and the obtained GLPs structure was characterized by Fourier transform infrared spectrophotometer (FT-IR) and gel chromatography (GPC). Furthermore, the in vitro antioxidant activities of GLPs were investigated. In the end, density functional theory (DFT) was leveraged to gain preliminary insights into the molecular mechanism underpinning polysaccharide extraction facilitated by DES. Results unveiled that when the moisture content within DES was maintained at 50%, extraction was carried out at a temperature of 80 ℃ for 1 h, and the liquid-to-solid mass-volume ratio stood at 1:30 g/mL, the extraction yield of GLPs reached 9.20%±0.27%. FT-IR and GPC results showed that GLPs had typical polysaccharide structures in the 4000~500 cm⁻¹ regions, and the number average mass weight (Mn) of GLPs was 8057 Da with the polydispersity index (PDI) of 1.6. In the context of in vitro antioxidant activity experiments, when GLPs content was 5 mg/mL, the total reducing power was measured at 0.67±0.04. Notably, the IC₅₀ values for GLPs' scavenging capabilities against DPPH, OH, and ABTS⁺ free radicals were determined to be 2.366, 6.179, and 2.440 mg/mL, respectively. DES simulation analyses revealed a binding energy of 65.29 kcal/mol between DES and glucose, a substantially higher value compared to the binding energy observed between water and glucose (20.38 kcal/mol). The GLPs extraction by DES was facilitated through the pivotal role of triple hydrogen bond interactions. The findings in this study elucidated the intrinsic mechanism at molecular level that underscores the superior effectiveness of DES in comparison to traditional hot water extraction methods.