The invention provides a functional concrete admixture and a preparation method and application thereof. The functional concrete admixture is composed of epoxy modified polysiloxane, polypropylmethylsilsesquioxane, alkoxy silane, nano silica, nano titanium dioxide, fatty amine polyoxyethylene ether and polyoxyethylene fatty acid. Components of the functional concrete admixture are in effective combination, generate synergistic effects and overcome respective defects, transmission of erosion media in a severe environment is efficiently inhibited, concrete electric flux is decreased, chlorine salt erosion resistance of concrete is improved, and accordingly durability of concrete is improved remarkably.