The invention discloses a formula of a special completely mixed pellet feed for fattening sheep and a preparation method. The formula comprises corns, barley straws, sunflower cakes, alfalfa meal, cottonseed meal, wheat middling, malt roots, soybean meal, stone powders, molasses, puffing urea, baking soda, salt, 0.2% of polymineral for mutton sheep, calcium hydrogen phosphate, multivitamins for mutton sheep, monensin, a sweetener and a flavouring agent, wherein nutrients comprise dry matters, crude protein, calcium, total phosphorus, the salt, digestible energy for sheep and coarse fiber. The preparation method comprises the steps of: mixing the stone powder, the baking soda, the salt, the 0.2% of polymineral for mutton sheep, the calcium hydrogen phosphate, the multivitamins for mutton sheep, the monensin, the sweetener and the flavouring agent to prepare a semi-finished product A; grinding the corns, the sunflower cakes, the alfalfa meal, the puffing urea, the cottonseed meal, the wheat middling, the malt root, the soybean meal and the barley straws; and evenly mixing the materials by adopting a mixing machine, preparing the materials to be granular through a granulating process, and spraying the molasses on the surface of the pellet feed through a spraying process. The special completely mixed pellet feed for fattening sheep accords with the national green food concept, and has a good development prospect.