The microvoid activated carbon with large specific surface area was prepared from reed pulping black liquor through chemical activation with K2CO3 as activator. The effect of activation temperature on the specific surface area, micropore volume and mesopore volume of the prepared activated carbon BET was closely investigated. The optimum temperature for preparing large specific surface area activated carbon is 800℃. The BET surface area and pore volume of the carbon activated at 800℃ were 1401 m2/g and 0.79 ml/g respectively. XRD shows that silicon crystals appeared in the activated carbon. The activated carbon had a good adsorption of heavy metal C(rVI)at pH=7 and the maximum adsorptive capacity could reach 54.23 mg/g and Langmuir model was better for describing the adsorption process than Freundlich model.