The invention discloses a preparation method of tetrabutyl urea, and the process is carried out by taking bi(trichloromethyl) carbonic ester and dibutyl amine in double solvents, wherein due to regulation and control of temperature, reactants and products are prompted to transfer in the solvents, so that reaction is carried out more completely; and high-purity tetrabutyl urea can be obtained through post-processing. The preparation method of tetrabutyl urea disclosed by the invention is low in toxicity of synthetic raw materials, high in product yield, good in quality, safe and reliable for production and applicable to large-scale production.