Iron-based modified biochar was directionally modified with humic acid (HA), and a fixed-bed adsorption device was used to investigate its mercury removal performance. The mercury removal performance of iron-based modified biochar under different loadings of HA was explored. The pore structure, valence state of surface elements and composition of surface functional groups of the biochar after directional modification were investigated by BET, XPS and FTIR. The microscopic morphology of the biochar was explored by scanning electron microscopy, and the distribution of active metal components on the surface of the biochar was analyzed by energy dispersive spectroscopy (EDS). The experimental results showed that the mercury removal performance of biochar after the directional modification of iron-based modified biochar with HA was greatly improved. The biochar coated with 5% HA by mass had the highest mercury removal performance, and the cumulative mercury adsorption is 18025ng/g every 3h, which is 65% higher than that of the iron-based modified biochar without HA. The biochar loaded with humic acid is mainly mesoporous, and the types of surface active metals are abundant, which is conducive to the oxidation of elemental mercury. The biochar loaded with HA has an increased number of oxygen-containing functional groups, such as carboxyl and alcoholic hydroxyl groups. After directional modification, a large number of amino groups and other nitrogen-containing functional groups that were beneficial to the adsorption of heavy metals appear on the surface of the biochar. The surface of the biochar exhibited agglomeration after directional modification. When the HA was overloaded, it completely covered the active sites on the biochar surface. It hinderd the redox reaction and was not conducive to the further oxidation of mercury. The process of removing mercury on the surface of biochar involves both chemical adsorption and physical adsorption.