The invention belongs to the technical field of organic photoelectric materials, and relates to a preparation method of an organic electroluminescent material (O-MeO-DMBI-I). The preparation method comprises following steps: (1) fully mixing 2-(2-hydroxyphenyl) benzimidazole, a potassium hydroxide solution, and methanol, dropwise adding methyl iodide under the protection of inert gas, and carryingout reactions for 12 hours at a room temperature to obtain a reaction solution; (2) filtering the reaction solution to obtain a filter cake, and drying the filter cake in vacuum to obtain dry powder;and (3) making dry powder go through a chromatographic column, and leaching the chromatographic column by a mixed solution of petroleum ether and ethyl acetate to obtain white crystals. The preparation method has the advantages of low raw material cost, mild reaction conditions, and high product yield, and is suitable for enlarged production.