The invention provides a synthesis method of tetrabutylurea. The synthesis method comprises the following steps: dissolving an organic strong base catalyst and dimethyl carbonate into a solvent; raising temperature to 30 DEG C to 50 DEG C to obtain mixed liquid; dropwise adding dibutylamine into the mixed liquid at 50 DEG C to 80 DEG C; after dropwise adding, heating to reflux and keeping the heat and reacting for 5h to 8h to obtain reaction liquid; rectifying the reaction liquid under normal pressure to obtain condensed liquid containing the solvent and residual liquid; decompressing and rectifying the residual liquid to obtain a tetrabutylurea product and residues. According to the synthesis method of the tetrabutylurea, provided by the invention, a toxic raw material, namely phosgene, is not used and hydrogen chloride gas is not generated, so that equipment is not corroded and requirements on the equipment are relatively low; meanwhile, three wastes are avoided; the mass content of the tetrabutylurea in an obtained tetrabutylurea product is 99 percent or more and the yield is 75 percent or more.