The effects of pyrolysis temperature,pyrolysis rate and other conditions on the activity of biomass char in the process of biomass char preparation were analyzed. The results showed that surface area and pore structure firstly increased and then decreased with the increase of the pyrolysis temperature. The pore structure was better under quickly pyrolysis than slowly pyrolysis. Biomass char can have the better adsorbability by modified and deashing that was called activated char. Biomass activated char were applied on dye wastewater treatment and flue gas demercuration.