Abstract: In order to study the influence of reactant concentration on the formation of ammonium bisulfate and ammonium sulfate, a simulating flue gas system with a more accurate composition of SO₃ was established. The starting temperature of ammonium bisulfate is about 230-270℃ and the peak temperature is about 180-240℃ under the experimental condition. The starting temperature and peak temperature of ammonium sulfate are about 40℃ lower than that of ammonium bisulfate. The formation of ammonium bisulfate is obviously higher than that of ammonium sulfate. With different concentration and molar ratio of NH₃ and SO₃, the formation rate of ammonium bisulfate is about 64%-90%, about 6-10 times of that of ammonium sulfate with about 6%-15% at 120℃. The increase of reactant concentration can promote the formation of both ammonium bisulfate and ammonium sulfate. And SO₃ is more conducive to the formation of ammonium bisulfate than NH₃. Further analysis shows that the variation curve of the generation fraction of ammonium bisulfate and ammonium sulfate with temperature presents a single peak. As the reactant concentration increases, the temperature range at which the peak is located increases gradually.