Process for one-pot liquefaction of biomass, comprising the following steps: preparing a slurry containing a catalyst, a vulcanizing agent and a biomass, and introducing hydrogen into the slurry to carry out a reaction under a pressure of 15-25MPa and a temperature of 380-480 °C, thereby obtaining a bio-oil; wherein, the slurry is prepared with using straw as the biomass according to the following steps: subjecting the straw sequentially to drying, a first pulverization, compression and a second pulverization to obtain a pretreated biomass, wherein said drying is carried out at a temperature of 50-70 °C for a period of 3-5h to obtain a dried straw having a moisture content of less than 2wt%; said first pulverization produces a median particle size of 100-300 μm, said compression is carried out under a pressure of 0.5-3MPa and a temperature of 30-60 °C, and said second pulverization produces a median particle size of 30-50μm and a bulk density of 400-500kg/m 3, mixing the pretreated biomass with the catalyst and the vulcanizing agent to obtain a mixture, and adding the mixture to an oil to carry out grinding pulping to obtain the slurry having a straw concentration of 30 wt% to 60 wt%, preferably 55 wt% to 60 wt%. preparing a slurry containing a catalyst, a vulcanizing agent and a biomass, and introducing hydrogen into the slurry to carry out a reaction under a pressure of 15-25MPa and a temperature of 380-480 °C, thereby obtaining a bio-oil; wherein, the slurry is prepared with using straw as the biomass according to the following steps: subjecting the straw sequentially to drying, a first pulverization, compression and a second pulverization to obtain a pretreated biomass, wherein said drying is carried out at a temperature of 50-70 °C for a period of 3-5h to obtain a dried straw having a moisture content of less than 2wt%; said first pulverization produces a median particle size of 100-300 μm, said compression is carried out under a pressure of 0.5-3MPa and a temperature of 30-60 °C, and said second pulverization produces a median particle size of 30-50μm and a bulk density of 400-500kg/m 3, mixing the pretreated biomass with the catalyst and the vulcanizing agent to obtain a mixture, and adding the mixture to an oil to carry out grinding pulping to obtain the slurry having a straw concentration of 30 wt% to 60 wt%, preferably 55 wt% to 60 wt%. subjecting the straw sequentially to drying, a first pulverization, compression and a second pulverization to obtain a pretreated biomass, wherein said drying is carried out at a temperature of 50-70 °C for a period of 3-5h to obtain a dried straw having a moisture content of less than 2wt%; said first pulverization produces a median particle size of 100-300 μm, said compression is carried out under a pressure of 0.5-3MPa and a temperature of 30-60 °C, and said second pulverization produces a median particle size of 30-50μm and a bulk density of 400-500kg/m 3, mixing the pretreated biomass with the catalyst and the vulcanizing agent to obtain a mixture, and adding the mixture to an oil to carry out grinding pulping to obtain the slurry having a straw concentration of 30 wt% to 60 wt%, preferably 55 wt% to 60 wt%.