Abstract: Composite adsorbents were prepared using a combination of modified biochar and MOFs through an in-situ growth method. The modified biocoke was doped with Fe/Cu polymetallic and Cu-BTC, both containing unsaturated metal centers and oxygen-containing functional groups. The study focused on identifying the Hg⁰ removal characteristics, investigating the coupling and synergistic mechanisms between Cu-BTC and modified biochar, and examining the various types of active centers present. A molecular structure model of the composite adsorbent was developed based on microscopic properties, and theoretical calculations of the Hg⁰ adsorption process were conducted using density functional theory, and fractional-wave state density function to uncover the underlying mechanisms of mercury removal and key actions. The study revealed that the Cu-BTC material exhibited better mercury removal performance compared to modified biocoke. Furthermore, the mercury removal efficiency of Cu-BTC-based modified biochar samples, resulting from a combination of the two materials, was significantly enhanced. The optimal loading ratio was found to be 50%, leading to a remarkable mercury removal performance of 239.18 μg/g. The molecular model of the composite adsorbent primarily consisted of aromatic structures, including two pyridinium azobenzenes, one anthracene benzene, and one anthracene benzene. The synergistic effect of polymetallic clusters, oxygen vacancies, and carbon skeleton facilitated the exposure of active centers. Moreover, the modified biochar acted as a substrate carrier, providing additional metal centers and carbon skeletons within the crosslinked MOFs structure, thereby enhancing electron acceptor and transfer capacities of the reaction system. By improving the electron acceptor capacity and mass transfer ability of the system, the formation of highly dispersed metal centers was promoted during heat treatment, preventing self-aggregation of metal oxide particles and synergistically enhancing Hg⁰ removal.