Abstract: The activated carbon was used as catalyzer and the ammonia as reducer to study the factors affecting NO_x conversion efficiency,such as temperature, O_xygen content,SO₂ and H₂O,etc.The mechanism of the low-temperature selective catalytic reduction(SCR) of NO_x over activated carbon was studied with transient response technique.The results show that at the experimental condition,NO_x conversion efficiency gradually decreases with the increase of the temperature,and gradually increases with the increase of O_xygen content.But the conversion efficiency increases slowly when O_xygen content is more than 2.5%.This shows that the activated carbon has favorable low-temperature SCR activity.The adding of O_xygen could promote catalytic reduction of NO_x.The reduction rate could be enhanced by pre-O_xidizing NO to NO₂.The effect of the SO₂ was less in a short time,but the SCR activity decreased when the H₂O was added and the activated carbon was poisoned.The experiment indicated that the SCR was in the mechanism of Eley-Rideal,and the NH₃ adsorption is the controlling step of the whole process.