The invention discloses a mutton sheep fattening feed and a preparation method thereof, and belongs to the technical field of animal feeds. The feed contains the following components in parts by weight: 90-110 parts of corn, 25-35 parts of cottonseed meal, 15-20 parts of rice bran, 3-5 parts of folium artemisiae argyi, 1-3 parts of a bamboo charcoal powder, 1-3 parts of codonopsis pilosula, 0.5-2 parts of cistanche deserticola, 2-4 parts of hawthorn, 3-5 parts of liquorice, 0.1-0.5 part of calcium hydrogen phosphate, 0.5-1 part of iodized salt, 10-20 parts of tomato pomace, 5-12 parts of alfalfa, 2-7 parts of a green tea powder, 0.01-0.1 part of zinc sulfate, 0.01-0.1 part of ferrous sulfate, 1-3 parts of a kelp powder, and 0.5-1 part of baking soda. The feed has balanced nutrition, can promote the fattening speed of mutton sheep, has the weight gained significantly, improves the slaughtering rate, and has good economic benefits.