The invention discloses a method for producing fuel oil by biomass hydrothermal liquefaction. The method is characterized by comprising the following steps: fully mixing a biomass raw material and solvent water (or adding catalyst water solution) to prepare seriflux, wherein a mass ratio of a catalyst to the raw material is 1:10 to 1:50, and the mass ratio of the raw material to water is 1:2 to 1:8; performing a reaction in a slurry bed reactor under a reducing atmosphere; controlling a liquefaction reaction temperature between 300 and 450 DEG C, a reaction pressure between 5 and 30 MPa and reaction time between 5 and 40 minutes; after the reaction, separating a product to obtain the fuel oil, solid residue, water, gas and the like. The method has the advantages of achieving complete biomass conversion, high oil product productivity, obtaining an oil product with a heat value equal to that of standard oil, relieving dependence on fossil energy, contributing to environment protection, lowering production cost and achieving good social and economic benefits.