The invention relates to a veterinary antiviral injection and a preparation method thereof. The veterinary antiviral injection is prepared through mixing, by weight, 40-60 parts of mango leaves, 20-40 parts of Artemisia carvifolia, 10-15 parts of reed rhizome, 5 parts of licorice root, 5-10 parts of licorice root, 0.1-0.3 parts of an antiseptic, and 0.1-0.3 parts of tween80. The preparation method comprises the following steps: cleaning above components, drying the cleaned components, crushing the dried components to obtain 40-60 mesh powder, adding purified water and an ether and ethanol mixture, carrying out ultrasonic extraction, clarifying the obtained extract, filtering the clarified extract, concentrating the obtained filtrate, adding the antiseptic, disinfecting the obtained product, and packaging the disinfected product to obtain the veterinary antiviral injection. The veterinary antiviral injection contains mangiferin, chlorogenic acid, flavones, artemisinin and immune substances, can be used to prevent and treat various viral diseases of livestock, is especially suitable for nonreactive pig raising, and also has a substantial disease prevention and treatment effect, and the preparation method has the advantages of simplicity, energy and time saving, and easy realization of industrial production.