Abstract: In order to reveal the concentration distribution of H₂S in the boiler water wall at different loads,the change of the atmosphere when the load changes,the relationship between H₂S and the furnace components CO and SO₂,the distribution of H₂S in the coking area and the influence of operation adjustment on H₂S and NO_x,and to guide the operation of the boiler,an on-line monitoring device for the water wall atmosphere was installed on a 300 MW level power plant boiler.The formation law of reducing components such as H₂S and CO near the furnace wall and the influence of operation adjustment on the atmosphere in the furnace were systematically studied.The results show that:（1） The overall concentration of H₂S and CO in the furnace is higher at high load,and the higher the load,the more serious the corrosion tendency.（2） When the load decreases from high to low,there is a critical load （40%BMCR）.When the load decreases to this critical load,the wall atmosphere begins to change from reducing atmosphere to oxidizing atmosphere.The furnace is prone to high temperature corrosion load range of 60%～100%.（3） On the whole,H₂S and CO on the wal showed a positive correlation,while H₂S and SO₂showed a negative correlation,but at the same time showed a certain degree of independence.（4） The average concentration of H₂S in coking area is 537×10^-6higher than that in non-coking area,which is consistent with the phenomenon that the corrosion of water wall in coking area is more serious than that in non-coking area.（5） Turning off the number of over-fire air layers and increasing the operating oxygen can significantly reduce the concentration of H₂S,with a maximum decrease of 91.4%.However,the decrease of H₂S concentration will cause the increase of NO_x.Turning off one layer of over-fire air can increase NO_xby an average of 109 mg/m~3.It is suggested that this contradiction needs to be balanced in actual operation.