The invention discloses a preparation method and application of a vascular plant based porous oxidative polymerization chelating adsorption material. The adsorption material takes a porous vascular plant as the carrier, and is grafted with a lot of amidoxime groups. The preparation method includes: subjecting the vascular plant to oxidation treatment, then conducting coupling with a double-bond equipped silane coupling agent, then carrying out free radical polymerization reaction with acrylonitrile under the action of an initiator, and finally converting part of a nitrile group into an amidoxime group through hydroxylamine, thus obtaining the adsorption material. The adsorption material has strong hydrophilicity, abundant porous structure and numerous amidoxime groups, and can be applied to removal of heavy metals or radioactive metallic elements from wastewater. The adsorption material shows the characteristics of high adsorption capacity, strong adsorption ability, reproducibility and reusability, and good reuse effect, and is especially suitable for adsorption removal of lead, cadmium, uranium and other metals from wastewater.