The invention discloses a veterinary medicine for preventing and treating chicken bursal disease and its preparation method and application. The veterinary medicine comprises the following components in parts by mass: 100-300 parts of astragalus, 100-300 parts of white peony, wheat 50-250 parts of winter, 50-200 parts of Epimedium, 50-200 parts of Ligustrum lucidum, 50-150 parts of Radix Isatidis, and 30-80 parts of freeze-dried fruit powder of Sorbus nigra. The preparation method of the veterinary drug is as follows: (1) weighing the traditional Chinese medicines except the freeze-dried fruit powder of Aronia nigricarpa according to the mass fraction, pulverizing them, adding enzymes for enzymolysis to obtain the enzymolysis solution; (2) ultrasonically extracting the enzymolysis solution , solid-liquid separation, adding water to the solid, ultrasonic extraction, filtering, to obtain the filtrate; centrifuging the filtrate while it is hot, to obtain the supernatant; (3) heating the supernatant, lyophilizing after vacuum concentration, pulverizing, and adding to it Add Sorbus nigra, mix well, and serve. Compared with the prior art, the present invention can effectively improve the activity of veterinary medicine by adding Aronia nigra at the end.