Abstract: In order to improve the adsorption capacity of bentonite, polyethyleneimine (PEI) was introduced onto the surface of 3-aminopropyltriethoxysilane (APTES)-modified bentonite (APTES/Bent) by crosslinking reaction to prepare PEI-crosslinked bentonite (PEI-APTES/Bent-4), which was characterised by FTIR, XRD and SEM. Taking Cr(VI) in water as the adsorption target, the adsorption performance of PEI-APTES/Bent-4 was investigated, and its adsorption mechanism and recyclability were explored. The results showed that PEI was successfully grafted onto the surface of bentonite, and the abundant active groups of PEI dramatically promoted the removal of Cr(VI). The optimum pH for adsorption was 2, and the adsorption capacity decreased with increasing pH. The adsorption of Cr(VI) by PEI-APTES/Bent-4 conformed to the Langmuir isotherm model and pseudo-second-order kinetic model, and the adsorption process was chemical adsorption and monolayer adsorption. The maximum theoretical adsorption capacity reached 137.50 mg·g⁻¹ at 313 K. Thermodynamic studies indicated that the adsorption was a spontaneous endothermic process. Based on the adsorption experiments, FTIR and XPS analysis, it is speculated that the adsorption mechanism of PEI-APTES/Bent-4 for Cr(VI) is mainly electrostatic interaction, reduction, and chelation. After six cycles, the adsorbent still maintained good adsorption performance. PEI-APTES/Bent-4 has broad application prospects for the removal of Cr(VI) from water.