The invention provides a preparation method of a fermentation state copper feed additive. The preparation method comprises the following steps: firstly preparing a fermentation substrate by taking alcohol industry yellow water, bran, powder dregs, corn flour and other industrial and agricultural side products as raw materials, then performing microbiological screening and acclimatization and culture to obtain copper-rich microorganism, inoculating to the prepared fermentation substrate and fermenting, and drying, grinding and packaging the fermented materials to obtain the fermentation state copper feed additive. Compared with the chemically synthesized copper feed additive, the fermentation state copper feed additive adopts the powder dregs, bran, alcohol industry yellow water and other side products as culture raw materials and substrates, so that the resource utilization is increased, the production cost of the copper feed additive is lowered, and the prepared fermentation state copper feed additive is more stable in bioavailability and higher in absorption rate, and the copper absorption rate is 19.2% or higher which is three times that of anhydrous copper sulfate.