The invention discloses a feed regulating agent for producing DHA (ducosahexenoic acid)-enriched milk as well as a preparation method of the regulating agent and a feed containing the regulating agent. The feed regulating agent is prepared from a plurality of nutrients, multiple Chinese herbal medicine raw materials, metallothionein crude extract powder as well as pine needle meal, mulberry leaf powder, murdannia triquetra powder and alfalfa powder at a certain proportion; the feed is prepared from the regulating agent and conventional feed raw materials at a certain proportion. The feed regulating agent for producing the DHA-enriched milk and the feed containing the regulating agent are reasonable in formula, wide in raw material source, low in cost, feasible in method, convenient and simple to operate, and free from any antibiotic and chemical medicine, free from residue and pollution, and free from adverse impact on color, smell and taste of the milk; the feed regulating agent can effectively improve physiological function of dairy cow, enhance immune function of dairy cow body and improve milk output and milk quality of the dairy cow, and can especially enhance DHA content and breeding benefit of the milk; the feed regulating agent is especially suitable for large-scale dairy industry production.