The invention discloses a porous carbon adsorbent as well as a preparation method and an application thereof. The active ingredients of the adsorbent refer to amorphous carbon and metallic oxides, wherein the mass ratio of the amorphous carbon to metallic oxides is (1-10):1. The preparation method comprises the following steps: dipping a natural high polymer material in a nitrate aqueous solution, drying, and carbonizing, thereby obtaining the porous carbon adsorbent. The porous carbon adsorbent disclosed by the invention has an excellent adsorption effect and has an effect of enhancing the adsorption effect on anionic inorganic pollutants. A natural and cheap high polymer material serves as a carbon source, can be conveniently processed into various shapes and is convenient to use; and in the test of low-concentration contaminated water samples, the adsorption effect of the porous carbon adsorbent is obviously superior to that of a commercial activated carbon adsorbent, straws, rice husk, coconut shells and other agricultural wastes can be utilized, the cost is low, and waste materials are changed into valuable things.