A preparing method of an aliphatic polycarbonate is provided to synthesize oligomer monomers by a transesterification reaction of carbonic acid dialkyl esters and aliphatic diols with accelerants in an atmosphere of a protective gas, and generate an aliphatic polycarbonate polymer by a polycondensation reaction of the oligomer monomers in a condition of high temperature and low pressure. According to the disclosure, environmentally friendly compounds with low boiling points and low costs are utilized as the accelerants to substitute the enzyme or acid-base catalysts to prepare aliphatic polycarbonate polymers in the prior art, and the cost is reduced; meanwhile, in the process of generating the aliphatic polycarbonate polymers, the accelerants can be removed from the reaction system along with the pressure reduced in the reaction system. The synthesis system is simple; moreover, the aliphatic polycarbonate obtained by the preparing method provided by the disclosure has merits such as superior colors.