To study the mechanism of SO 2 and Hg removal from flue gas, an experimental packed bed reactor was designed to simulate the dry FGD, where a mixture of lime and fly ash in ratio 1:3 w/w was used as the SO 2 and Hg sorbent, and steam at temperature of 100℃ was applied for activation of the sorbent, while the activation time set to 20 min. The experimental factors including the SO 2 /Hg sorbent characteristics, 50% breakthrough time for SO 2 /Hg removal, sorbent packed bed depth and reaction temperature were investigated. The experimental results show that after steam activation, the BET specific surface area and specific pore volume increased from 37.8 to 45.5 m 2 /g and from 0.42 to 0.51 cm 3 /g, respectively. With activation of the sorbent by steam, the 50% breakthrough times of SO 2 and Hg removal increased from 34 to 42 min and from 23 to 45 min, respectively. When the packed bed depth was increased from 5 to 25 mm, the 50% breakthrough times for Hg and SO 2 removal increased from 12 to 52 min and from 6 to 47 min, respectively. With the increase of the reaction temperature, the 50% breakthrough of SO 2/Hg removal decreased accordingly. Steam activation can efficiently improve SO 2 /Hg removal simultaneously. To study the mechanism of SO 2 and Hg removal from flue gas, an experimental packed bed reactor was designed to simulate the dry FGD, where a mixture of lime and fly ash in ratio 1: 3 w / w was used as SO 2 and Hg sorbent, and steam at temperature of 100 ° C was applied for activation of the sorbent, while the activation time set to 20 min. The experimental factors include the SO 2 / Hg sorbent characteristics, 50% breakthrough time for SO 2 / Hg removal, The experimental results show that after steam activation, the BET specific surface area and specific pore volume increased from 37.8 to 45.5 m 2 / g and from 0.42 to 0.51 cm 3 / g, respectively. With activation of the sorbent by steam, the 50% breakthrough times of SO2 and Hg removal increased from 34 to 42 min and from 23 to 45 min, respectively. When the packed bed depth was increased from 5 to 25 mm, the 50% breakthrough times for Hg and SO 2 removal increased fro With the increase of the reaction temperature, the 50% breakthrough of SO 2 / Hg removal decreased accordingly. Steam activation can efficiently improve SO 2 / Hg removal simultaneously.