The invention discloses a low-cost preparation method of polymethoxy dibutyl ether. The preparation method comprises the following steps: (1) mixing butanol with paraformaldehyde in a molar ratio of (1 to 1.5)-(1 to 2.5) so as to obtain a mixture, pumping the mixture into a reaction kettle, and reacting at a temperature of 70-180 DEG C and a pressure of 0.1MPa-2.0MPa under the action of an acid catalyst; (2) pumping a reactant obtained in the step (1) into a pressurizing rectifying tower, and separating polymethoxy dibutyl ether from the tower bottom, wherein the separation conditions are as follows: the tower top pressure is 0.1MPa-0.8MPa, the tower top temperature is 110-190 DEG C, the tower bottom pressure is 0.1MPa-0.8MPa, and the tower bottom temperature is 170-243 DEG C; and (3) carrying out purification and separation. By virtue of the preparation method, the yield and purity of polymethoxy dibutyl ether can be effectively increased, meanwhile, n-butyl alcohol can be extracted and recycled as much as possible, and the production cost is lowered.