The conditions for preparation of biomass carbon were studied with zinc chloride as an activating agent.Orthogonal optimization design was carried out considering different zinc chloride concentration,carbonizing temperature and time as influential factors,using various biomass material to prepare activated carbon and taking the value of methylene blue adsorption as an optimization index.Then,the biomass activated carbon with better performance was adopted to implement mercury adsorption experiments.The results show that the methylene blue adsorption value of soybean stem activated carbon is 0.15 mg/g,the mercury adsorption capacity in 4 hours is 0.015 mg and the penetration rate is 5.30%,at an optimal condition of 600 ℃ activation temperature,1.5 hours activation time and 50% zinc chloride concentration.Therefore,the methylene blue adsorption efficiency by activated carbon is different because of the effect of raw materials,the activator concentration,activation time,activation temperature and so on.The mercury adsorption efficiency of soybean straw activated carbon is the highest because of its porosity.