The invention relates to a novel biomass hydrothermal liquefaction bio-oil preparation method. An aluminum-water hydrogen producing reaction is used as a hydrogen supply source to be cooperated with corn stalk catalytic liquefaction for preparing bio-oil; the bio-oil quality can be improved; the method belongs to the technical field of environment protection and new energy sources. The aluminum-water hydrogen producing reaction is used as the hydrogen supply source to be cooperated with corn stalk catalytic liquefaction for preparing bio-oil; the aluminum water reaction hydrogen production and the biomass hydrothermal liquefaction are performed at the same time; the in-situ hydrogen supply modification refining is performed in the biomass liquefaction process; the bio-oil oxygen content can be effectively reduced; the thermal value is improved; the goal of improving the bio-oil quality is achieved.