The invention discloses a garlic straw and livestock raising combined feed additive. The garlic straw and livestock raising combined feed additive is prepared from, by weight, 40-80 parts of garlic straw, 0.03-0.07 part of compound enzymes, 0.01-0.05 part of saccharomycetes, 0.03-0.07 part of lactic acid bacteria, 5-9 parts of oysters, 1-3 parts of radix polygoni multiflori, 1-4 parts of the seedof Chinese dodder, 0.3-2 parts of caulis spatholobi, 0.3-2 parts of radix morindae officinalis, 0.3-2 parts of cloves, 0.3-2 parts of parasitic loranthus, 0.3-1.5 parts of cortex acanthopanacis, 0.3-1.5 parts of teasel roots, 5-15 parts of pollen extract and 0.5-4 parts of chitosan oligosaccharide. The invention further provides a preparation method of the feed additive and a use method of the feed additive. The feed additives accounts for 0.05% to 0.3% (w/w) of feed. A compound enzyme system and microorganisms are used for acting on the straw, the oysters and other traditional Chinese medicine and chitosan oligosaccharide achieves a synergistic effect, the disease-resistant immunity of livestock and poultry is improved, zinc-rich ingredients are provided, the feed additive can be absorbedby the intestines and stomach easily, flocks, herbs and other livestock and poultry are robust in body, and the feeding cost is reduced; therefore, the effects of saving grain, reducing excrement emissions, increasing the weight of the livestock and poultry, improving feed flavor and the like are achieved.