Abstract: In the field of heavy metal pollution remediation, modified biochar has emerged as a crucial material for the removal of heavy metal ions from water and soil due to its wide availability, excellent adsorption performance, and environmental friendliness. However, constrained by the resolution of characterization techniques and the complexity of interaction processes, the adsorption mechanisms of modified biochar for heavy metal ions have not yet been systematically understood. Based on quantum chemical molecular simulations and visual analysis methods, this study systematically investigates the interaction mechanisms between ZnCl₂-modified corn stalk biochar (ZBC) and Cd²⁺ at the molecular level. It identifies the active sites on the ZBC molecular surface involved in adsorption and analyzes the differences in interaction strength between these sites and Cd²⁺. The results indicate that the primary mechanisms for Cd²⁺ adsorption by ZBC are functional group-mediated weak ionic bonding and cation-π interactions. Elucidating the adsorption mechanism at the molecular level, this study provides theoretical guidance for promoting the practical application of modified biochar in heavy metal pollution remediation.