The invention discloses a method for preparing complete feed for cattle and sheep by using mushroom medium residues as a raw material for secondary fermentation. The complete feed is prepared from the following raw materials in parts by weight: 20-35 parts of mushroom medium residues, 25-40 parts of a plant material, 8-10 parts of corn flour, 5-8 parts of rice bran, 3-5 parts of bean pulp, 3-4 parts of sweet potatoes, 2-3 parts of honey, 0.1-1 part of a fermentation strain and 0.1-0.3 part of trace elements, wherein the plant material is one or mixture of more than one of sugar cane tops, corn stalks, fresh pasture, wheat-straws, rice straws, paper mulberry, peanut vines and weeds. The mushroom medium residues are fermented to prepare feed for cattle and sheep with simple preparation method and low cost; and the feed prepared after fermentation has comprehensive nutrition and sweet taste, can be used for improving the appetite of cattle and sheep, and can be well accepted by cattle and sheep, so that cattle and sheep grow fast.