The invention provides a biodiesel-based alcoholic fuel oil, which consists of the following substances in percentage by mass: 20 to 50 percent of refined biodiesel, 40 to 80 percent of industrial methanol and 5 to 30 percent of additive, wherein the additive comprises 5 to 20 percent of solvent aid, 1 to 15 percent of cosurfactant, 0.2 to 2 percent of stabilizer and 0.1 to 1 percent of corrosion inhibitor. A preparation method comprises the following steps of: mixing the substances in percentage by mass, and stirring the mixture uniformly at normal temperature to obtain the fuel oil. The fuel oil has the advantages of low cost, high heat value and stable performance; the preparation method has the advantages of simple process, convenience and safety of use and good adaptability to the boiler; and compared with diesel oil, the fuel oil is economic and energy-saving, has low environmental pollution, is regenerative energy, and can be used as commercial oil for great popularization and use.