The invention discloses a catalyst zinc oxide and a preparation method thereof, the preparation method comprises the following steps: dissolving zinc salt in an aqueous solution, after reaching saturation, preparing a zinc chloride saturated solution, placing the zinc chloride saturated solution in a semi-permeable membrane apparatus, filtering to obtain a diluted hydrochloric acid solution with same pH value of a mother liquor, adding an auxiliary agent for keeping viscosity and system stabilization of the mother liquor, controlling the temperature of the mother liquor between 0 and 5 DEG C, stopping dialysis when pH value is 5.5, using ammoniacal liquor to neutralize the pH value of the mother liquor to 7 to obtain a catalyst zinc oxide II type product, mixing the catalyst zinc oxide II type product and silica sol with minute quantity, adding a flocculating agent after mixing is complete, filtering after flocculation to obtain a filter cake, drying the filter cake, and fully calcining to obtain the catalyst zinc oxide. The catalyst zinc oxide improves the preparation method of nano zinc oxide in our country and fills the blank for production of the catalyst zinc oxide, during the preparation process, the method has the advantages of low energy consumption, saved cost, automation work realization, good stability and convenient maintenance.