Polyethyleneimine-modified magnetic bentonite (PEI/KH560/MBent) was prepared by grafting polyethyleneimine (PEI) on the surface of magnetic bentonite (MBent) and characterized by FTIR, VSM, XRD, TGA, EA, SEM and EDS. The adsorption performance of PEI/KH560/MBent for Pb_²⁺ and Cu_²⁺ in aqueous solution was studied. The results showed that polyethyleneimine was successfully grafted onto the surface of magnetic bentonite and effectively increased the adsorption capacity for Pb_^2??+ and Cu_²⁺. The initial pH of solution had a great influence on the adsorption capacity. When the pH increased, the adsorption capacity increased. Under the conditions of pH=5 and the initial concentration of the solution of 300 mg/L, the actual adsorption capacities of PEI/KH560/MBent for Pb_{^{2 ??+}} and Cu_²⁺ were 96.21 and 61.08 mg/g, respectively. The adsorption process was more in line with the quasi-second-order kinetic model, and the adsorption behavior was more consistent with the Langmuir adsorption isotherm model. The results of thermodynamic studies indicated that the adsorption was a spontaneous endothermic process. After 5 cycles of recycling, the adsorption capacity remained above 60% of the original, indicating that PEI/KH560/MBent had certain reusability.