The invention discloses a nano gelatin/polymer composite fiber belt preparation method based on seawater uranium extraction. The preparation method comprises following steps: step one, preparing a nano gelatin/polymer fiber belt: individually dissolving gelatin and polymers, then mixing two solutions according to a certain ratio, evenly stirring to obtain a spinning solution, carrying out electrostatic spinning, drying, and cutting to obtain the nano gelatin/polymer fiber belt; and step two, curing tannin, soaking the nano gelatin/polymer fiber belt in a tannin water solution for 1 to 10 hours, taking out the fiber belt, then transferring the fiber belt to distilled water, stirring, adding a crosslinking agent, carrying out crosslinking for 2 to 6 hours at a temperature of 20 to 50 DEG C,taking out the fiber belt, washing, and drying to obtain the nano gelatin/polymer composite fiber belt with cured tannin. The fiber belt is prepared by weaving nano level fibers; the diameter is small, the specific surface area is large, the amount of cured tannin is large; the provided fiber belt has an extremely high adsorbing performance on low concentration uranium, moreover, the hydraulic performance, floating property, and water surging performance of the fiber belt are good, and thus the fiber belt can be used to separate and enrich uranium in seawater, salt lakes, and radioactive wastewater.