As a supporting material in the high-tech field, the distribution of indium in the earth's crust is small and scattered. An efficient material is required to selectively adsorb indium from the leaching of other minerals and secondary resources. In this study, an adsorbent phytic acid–hyperbranched polyethyleneimine–oxidized carbon fiber (PA–HPEI–OACF) was prepared by modifying carbon fibers with hyperbranched polyethyleneimine (HPEI) and phytic acid (PA) for the efficient adsorption and separation of In(III) in hydrochloric acid media. The adsorption and separation of absorbents was investigated using static adsorption. The adsorption mechanism of absorbents for In(III) was determined by XPS. The maximum adsorption capacity of PA–HPEI–OACF for In(III) was 34.21 mg L⁻¹ at 298 K and pH of 3.5. The adsorption process of PA–HPEI–OACF for In(III) conforms to the pseudo-second-order kinetic model and involves an endothermic reaction. The adsorption isotherm follows the Freundlich isotherm adsorption model. In the In(III), Fe(II), Cu(II), and Zn(II) mixed solution, PA–HPEI–OACF only adsorbed In(III) and Fe(II) at pH 3.5, and the selectivity coefficient of PA–HPEI–OACF for In(III) over Fe(II) was 798.81. The XPS analysis revealed that the adsorption of PA–HPEI–OACF for In(III) was the result of the combined action of amine groups and phosphate groups with In(III).