The invention relates to a feed additive capable of enhancing immunity and relieving transport stress of fattening pigs as well as a preparation method and an application of the feed additive and belongs to the feed field. The feed additive is prepared from, in parts by weight, 0.4-2 parts of plant extracts, 10-30 parts of coconut oil, 3-15 parts of rare earth-chitosamine chelate salt, 3-15 partsof zinc lactate and 38-83.6 parts of a carrier. The plant extracts comprise a macleaya cordata extract and a herba epimedii extract. The feed additive is safe, harmless, small in dosage, low in cost and stable in effect. The preparation method of the feed additive comprises the step of mixing the components of the feeding additive. The preparation method is simple and good in condition controllability. The feed additive can effectively enhance the immunity and disease resistance of the fattening pigs, improve intestinal health of the fattening pigs and relieve transport stress reactions afterbeing applied to preparation of fattening pig feed to feed the fattening pigs.