The invention relates to biomass fuel oil. The biomass fuel oil comprises the following components in percentage by weight: 10 to 15 percent of vegetable oil, 10 to 40 percent of bio-alcohol, 5 to 15 percent of bio-diesel, 0 to 5 percent of fatty acid, 5 to 15 percent of mutual solvent, 0 to 10 percent of combustion accelerant, 0.1 to 1 percent of solid base catalyst, 0.1 to 1 percent of combustion improver, 0.1 to 0.5 percent of oxygenate and 0.1 to 0.5 percent of detergent. A preparation method of the biomass fuel oil comprises the following steps of: a, adding and uniformly stirring the vegetable oil, the bio-alcohol and the mutual solvent in a reaction kettle, adding the solid base catalyst into the mixture and stirring the mixture to form suspension; and b, heating the suspension to 50 to 70 DEG C, making the suspension flow back through a condenser, stirring the obtained product for 10 to 90 minutes, cooling the product to the room temperature, filtering off the solid base catalyst, then sequentially adding the bio-diesel, the fatty acid, the combustion accelerant, the combustion improver, the oxygenate and the detergent and stirring and reacting the mixture for 20 to 30 minutes to obtain the biomass fuel oil. The biomass fuel oil provided by the invention has the advantages of high combustion value, high lubricating property and high flash point.