Abstract: A saturated cluster model was established for the washing biochar (WB) loaded with metal ions, based on which, the adsorption process of Hg⁰ on the surface of modified WB was studied using density functional theory. Results show that metal ions could be stably loaded on the surface of WB; the adsorption of Hg⁰ on the surface of modified WB is found to be the chemical kind according to the results of adsorption energy and Mulliken charge, and the metal ions could improve the adsorption capacity of WB for elemental mercury.