Abstract: Lignin, as the only renewable component rich in aromatic structures within biomass resources, presents efficient depolymerization and high-value utilization as key challenges in biomass energy applications. The research is aimed at achieving the hydrothermal depolymerization of lignin by using an ethanol-water mixed solvent as the reaction medium, coupled with an aqueous phase reforming reaction to enhance the quality of the depolymerized product （bio-oil）. Through investigation the influence of reaction conditions on the yield of depolymerization products, it is found that the highest yield of heavy oil of 52.47% from hydrothermal depolymerization of lignin is achieved at a temperature of 260 ℃, a reaction time of 60 min, and a solid-liquid ratio （lignin/solvent） of （1.5∶20） g/mL. Analysis of the light and heavy fractions of the depolymerized bio-oil shows that the heavy oil fraction predominantly contains G-type phenols （32.40%）, while also being rich in S-type phenols （17.12%） and ketone compounds （19.27%）, with a relatively low content of H-type phenol content （8.61%）. The light oil fraction is characterized by a high enrichment of G-type phenols （50.11%） and a significant proportion of aldehyde products （38.29%）. Furthermore, under optimal reforming conditions of 320 ℃ and 20 min, the aqueous phase reforming of heavy bio-oil achieves a maximum HHV of 34.21 MJ/kg, an effective hydrogen-to-carbon ratio （H/C_eff） of 1.02, and an energy recovery （R_e） as high as 86.31%. GC-MS analysis is employed to investigate the influence of varying heavy oil/water ratios on the component distribution of the reformed bio-oil. Results indicate that the heavy oil/aqueous ratio significantly influenced the product selectivity. As the ratio is increased from （1∶40） to （2∶40） g/mL, the relative content of phenolic and ketone products in the reformed bio-oil shows an overall upward trend. The phenolic product content rises from 50.08% to 63.88%, while ketone products increase from 1.19% to 14.63%. Conversely, ether and ester products exhibit a decreasing trend, with ether products decreasing from 12.57% to 1.37% and ester products decreasing from 21.42% to 11.96%. The study demonstrates that the ethanol-water co-solvent system not only facilitates efficient lignin depolymerization but also allows the aqueous phase to be recovered and reused in subsequent aqueous phase reforming processes. This integrated approach is shown to contribute to improved bio-oil quality and to offer a promising route for the high-value utilization of lignin resources.