As a rare metal, indium is an important component of ITO targets in liquid crystal displays (LCDs). In order to alleviate the problem of resource loss, the recycling of indium in waste LCDs has become more and more important. In this paper, the adsorbent (CM-HPEI-HD-1) was prepared by modifying the weakly acidic macroporous resin (HD-1) with hyperbranched polyethyleneimine (HPEI) and sodium chloroacetate. The adsorbent was characterized using SEM, XRD, FTIR, TGA, and XPS. And its adsorption performance for In(III) in the hydrochloric acid system was investigated. The experimental results showed that the maximum adsorption capacity of the CM-HPEI-HD-1 for In(III) was 97.78 mg g⁻¹ at 35 °C. Kinetic experiments showed that the adsorption of In(III) on CM-HPEI-HD-1 was in accordance with the pseudo-second-order kinetic model. The adsorption process is an endothermic process. The adsorption isotherm data were consistent with the Freundlich isotherm model. The cyclic performance of CM-HPEI-HD-1 was evaluated using the dynamic adsorption–desorption method. The cyclic experiments showed that the adsorption performance of the adsorbent remained basically unchanged after five adsorption–desorption cycles. The separation performance of the adsorbent for In(III) and Sn(II) was investigated, and it was found that the adsorbent had a better adsorption performance for In(III). In addition, the adsorption mechanism of In(III) on CM-HPEI-HD- was investigated based on XRD and XPS. It was found that both carboxyl groups and amine groups interact with In(III).