The invention provides a method and a device for preparing ZnO nano-particles by external electric-field induction. The method comprises the following steps of: adding a NaOH solution into a reaction vessel under a constant-temperature water bath; constantly applying an external electric field to the reaction vessel; dripping a zinc acetate (Zn(Ac)2.2H2O) solution into the NaOH solution and mixing at the same time; insulating the heat of the solution water bath for a period of time after finishing the dripping step; centrifugally separating powder after finishing the reaction; drying the powder after being washing 5 times; and obtaining the nano zinc-oxide powder. The device comprises the constant-temperature water bath, the reaction vessel for containing reactants, a feed hopper, an adjustable-speed stirrer, two parallel electrodes and a high-voltage electrostatic generator. The device has the advantages of low equipment requirement, low cost, simple operation, high utilization efficiency and short reaction time.