A preparation method of tetraacetylethylenediamine is provided. The method includes (1) adding ethylenediamine and a catalyst into a kettle, raising the temperature in a gradient manner, adding aceticacid dropwise into the kettle, and performing staged temperature maintaining and synthesis of N,N'-diacetylethylenediamine; (2) subjecting the reaction product of the step (1) to gradient temperatureraising, adding acetic anhydride in batches into the kettle, performing reaction at maintained temperature in different temperature gradients, subjecting the filtrate to vacuum external evaporation,and then performing cooling and crystallization, filtration, washing and drying to obtain tetraacetylethylenediamine crystals. According to the method, under a constant pressure, acylation reagents are added in batches at different reaction temperatures and staged temperature maintaining is performed, and vacuum external evaporation is performed after the reaction is finished to remove byproduct water and acetic acid. The method avoids a high amount of solvent and energy consumption for external evaporation at the same time of reaction in traditional methods, ensures concentrations of materials before a system reaches an equilibrium state, effectively increases the reaction yield, shortens the reaction times, reduces energy consumption and reduces the product production cost.