The invention relates to a catalyst used in ammonia-process integrated desulfurization and denitrification. The catalyst is a pyridine- or imidazole-type ionic liquid, which is easy and convenient to prepare. A catalyst system composed of the ionic liquid catalyst and non-water-soluble organic silicon is high in catalytic speed, is stable in catalytic performance and can be recycled, and has excellent industrial application prospect. The ammonia-process integrated desulfurization and denitrification method can quickly absorb and oxidize SO2 and NOx in flue gas to generate a salt solution containing ammonium sulfate and ammonium nitrate, thereby recycling the SO2 and the NOx to obtain resources. The catalyst system is less in use amount and can be recycled. The catalyst system is high in absorption efficiency on SO2 and NOx, is low in energy consumption and operation cost, and is green and environment-friendly.