The invention discloses a preparation method for zinc oxide nano particles, relating to the preparation field of inorganic nonmetal nanometer materials. The preparation method includes the steps as follows; firstly preparing zinc source dispersion solution and oxygen source dispersion solution; adding the oxygen source dispersion solution in the zinc source dispersion solution under the conditionof 70-80 DEG C and the dropping time of the oxygen source dispersion solution is 90-120 minutes; reacting to generate white precipitates; later, conducting centrifugal separation on reactant to obtain precipitates; washing, centrifugating and drying the obtained precipitates by distilled water, water-ethanol mixed liquor and absolute ethyl alcohol in sequence; and roasting the obtained precipitates for 3-5 hours at the temperature of 350-470 DEG C to obtain the zinc oxide nano particles. The preparation method has low cost, recyclability, simple equipment, simple and easily-controlled operation conditions, no environment pollution, no toxicity and no harm, and is convenient to large-scale production.