The invention discloses a preparation method of 3-(2,2,2-trimethylhydrazine)propionate dihydrate, belonging to the technical field of chemical synthesis. The method comprises the following steps: adding tert-butyl acrylate into a three-neck flask with a mechanical stirring and dropping funnel, dropwisely adding excessive 5-50% unsymmetrical dimethylhydrazine, and distilling out 3-(2,2-dimethylhydrazine)tert-butyl propionate while depressurizing; dissolving the distillation product in ethanol, introducing or dropwisely adding excessive 5-30% methylation reagent, and washing with cold ethanol to obtain 3-(2,2,2-trimethylhydrazine)tert-butyl propionate; dissolving the 3-(2,2,2-trimethylhydrazine)tert-butyl propionate in water, adding a small amount of acid, and heating under reflux for 1-3 hours; depressurizing to remove water and acid; and adding solvent and organic amines into the remainder, filtering, and recrystallizing the solid with 95% ethanol to obtain the target product. The invention converts the alkaline hydrolysis in the prior art into acidic hydrolysis and consumes less acid, and the acid can be removed by depressurized distillation; and the neutralization only needs a small amount of alkali, and the salt generated after neutralization can be dissolved in the solvent so as to be removed, so that the purity of the obtained product is high.