The invention relates to a poly-nanotube modified carbon fiber adsorbent as well as preparation and application thereof. Particularly, the invention discloses a carbon fiber adsorbent which comprises modified carbon fiber, wherein the modified carbon fiber comprises a carbon fiber base, a modified polymer membrane layer combined with the surface of the carbon fiber base, and a poly-nanotube modification layer which is combined with the surface of the modified polymer membrane layer. The invention further discloses a preparation method and application of the carbon fiber adsorbent. The carbon fiber adsorbent is excellent in adsorption property, can be recycled and is free of secondary pollution on water bodies, and a relatively optimal option can be provided for water body purification.