The invention discloses biomass methanol diesel oil. The biomass methanol diesel oil comprises the following components by weight: 100 parts of diesel oil, 40-60 parts of fatty acid methyl ester, 15-40 parts of methanol, and 2-20 parts of composite cosolvent. The biomass methanol diesel oil comprises the following steps: adding 100 parts by weight of diesel oil in a reactor with a stirring apparatus, a heating device, a thermometer and a constant pressure funnel, at 25-500 DEG C, adding 2-20 parts by weight of composite cosolvent, stirring the solution uniformly, gradually adding 40-60 parts by weight of fatty acid methyl ester and 15-40 parts of methanol based in the constant pressure funnel, stirring the mixture uniformly to form the homogeneous biomass methanol diesel oil which is thermodynamically stable. The biomass methanol diesel oil is wide in resource, relatively cheap, high in point of flammability, high in cetane number, and good in water resistance, environmental protection, high safety and renewability, and can be used to directly substitute the common diesel oil in fields.