The invention discloses bactericidal mildewproof down composite fibers prepared from the following raw materials in parts by weight: 11-14 parts of goose down superfine powder, 15-20 parts of puffed goose feather powder, 6-9 parts of kapok fibers, 8-12 parts of coconut palm fibers, 17-19 parts of sugarcane skins, 3-5 parts of bentonite, 5-8 parts of hollow vitrified micro bubbles, 1-3 parts of Chinese thorowax roots, 2-4 parts of white peony roots, 0.1-0.3 part of aluminum sulfate, 0.04-0.08 part of zinc oxide, 2.3-4.6 parts of polyacrylate, 0.05-0.08 part of sodium dodecylbenzene sulfonate, 1.2-3.5 parts of nano silicon dioxide, 100-120 parts of 1-butyl-3-methylimidazol acetate, 110-130 parts of 1-butyl-3-methylimidazol dibutylphosphoric acid ester, 1-3 parts of an auxiliary agent and an appropriate amount of water. The down composite fibers prepared by a method disclosed by the invention have relatively strong bacteriostatic, bactericidal, inflammation diminishing, deodorant and mildewproof effects, are irritation-free to skin, are lightweight and warm-keeping, and are deeply loved by consumers.