The invention discloses an aliphatic ester type ash-free antirust additive, which is an aliphatic ester compound prepared from saturated or unsaturated fatty acid and a polyhydroxy organic amine compound through an esterification reaction. The method for preparing the antirust additive comprises the following steps of: mixing 1 to 2 moles of saturated or unsaturated fatty acid with 1 mole of polyhydroxy organic amine compound, adding a proper amount of No.120 or No.200 solvent oil for the esterification reaction at the temperature of between 90 and 160 DEG C until a theoretical amount of water is dehydrated; and distilling to remove the solvent oil. The ash-free antirust additive has good dissolubility, antirust property and emulsion resistance, simultaneously has a lower acid value and a certain base value, and has wide application in the industrial lubricant.