In this paper, biomass charcoal was prepared with rice straw as raw material to remove mercury from the atmosphere. Then the biomass charcoal was modified with AgNO3 and KI solution. In order to optimize the experimental conditions, the effects of reaction temperature, carrier gas flow rate, and biomass charcoal dosage on the adsorption performance of Hg0 were investigated through the designed orthogonal tests. Finally, the adsorption mechanism of biomass charcoal towards Hg0 was studied on the basis of the adsorption dynamics. The experimental results show that the pore structure of the biomass charcoal changed significantly after modification with AgNO3 and KI solution. The average pore diameter, total pore volume, and mesoporous pore volume increased and the physical adsorption capacity was improved. The optimal conditions of the biomass charcoal for Hg0 adsorption were the reaction temperature of 40 ℃, the carrier gas flow rate of 1.5 L/min, and the biomass charcoal dosage of 2.0 g. The Hg0 adsorption capacity of the biomass charcoal modified by 2.0 mg/mL KI solution increased significantly, reached 2.498 mg/g.