The secondary grafting of acrylic acid and acrylamide onto ultra-high-molecular-weight polyethylene (UHMWPE) fibers was accomplished through ⁶⁰Co gamma-ray pre-irradiation, and UHMWPE fiber adsorbents containing hydroxamic, amide, and carboxyl groups were prepared through a hydroxamic reaction. The results of scanning electron microscope (SEM), attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and thermogravimetric analysis (TGA) all showed that acrylamide and acrylic acid were successfully grafted onto the fiber and that the hydroxamic reaction successfully converted the amide group into the hydroxamic group. Evaluation of the heavy metal ion adsorption performance indicated that the adsorption capacities of the UHMWPE fiber adsorbent for Cu(II), Co(II), and Ni(II) could reach 318 mg/g, 165 mg/g, and 140 mg/g, respectively (the adsorption concentration was 500 mg/L for 4 h). In the competitive adsorption of copper-cobalt-nickel mixed heavy metal ions, the removal rates of the copper, cobalt, and nickel ions were 99.5%, 43.5%, and 60.5%, respectively (the initial ion concentrations were all 200 mg/L and the amount of adsorbent used was 3 g/L).