The invention discloses base fluid for diluting semens of equus animals and a preparation method and a use method thereof. The base fluid contains A fluid and skimmed milk. The A fluid contains glucose, raffinose, D-glucopyranose, trisodium citrate, ppotassium citrate and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES). The preparation method for the base fluid includes weighing various components of the A fluid into a sterile beaker, adding double-distilled water, dissolving, bringing to volume, filtering, split charging, sterilizing, and sealing to obtain the A fluid, and adding same amount of the skimmed milk into the A fluid to be evenly mixed. Users can also add penicillin and dihydrostreptomycin to the base fluid or add penicillin, dihydrostreptomycin, yolk and glycerol into the base fluid. The base fluid is suitable for semen dilution and normal temperature preservation, low temperature preservation and freezing preservation of the semens of the equus animals. The base fluid for diluting semens of equus animals and the preparation method and the use method of the base fluid have the advantages of being simple to prepare, convenient to use, good in preservation effect of the semens of the equus animals, multi-purpose, time-saving, labor-saving and applicable to mass production and application.