Abstract: The influences of co-existing components including O₂, CO₂ and H₂O in flue gas on simultaneous desulfurization and denitrification using microwave irradiation over activated carbon are mainly studied in this paper. The results show that SO₂ inhibits the denitrification reaction on some extent. The water vapor in the flue gas has some inhibitory effect on desulfurization while accelerates the denitrification reaction. But once the moisture content is more than 9.0%, both the efficiencies of desulfurization and denitrification will decrease. The presences of O₂ and CO₂ can enhance the efficiencies of desulfurization and denitrification. But high concentrations of O₂ and CO₂ will cause the loss of activated carbon, thereby inhibit desulfurization and denitrization. Furthermore, the efficiency of removing SO₂ and NO_{x using this technique is higher than 90% and the reaction products are friendly to the environment. The results have a great value for the process optimization of simultaneous desulfurization and denitrification using microwave irradiation over activated carbon.}