In order to realize the ultra-low emission transformation of pelletizing flue gas, based on the research on grate-kiln manufacturing technique, the current status of particulate matter, SO₂ and NO_x emissions in flue gas is analyzed, and the technical measures of corresponding ultra-low emission are applied. The results show that the temperature at the second stage of preheating of the grate is 900~1 100 ℃. The process modification can reduce the NO_x in the flue gas by about 30% in the reaction temperature range of denitrification reducing agent; ozone cascade oxidation process transformation sprays the strong oxidant O₃ into the main flue to oxidize NO to NO₂, when n(O₃)/n(NO) (molar ratio) ≤1.0, the oxidation product of NO is NO₂, and with n(O₃)/n(NO) > 1.0, part of the NO₂ in the flue gas in the desulfurization tower is further oxidized to NO₃; At this time, NO₃ and NO₂ react rapidly to generate N₂O₅; According to the characteristics of high-valence NOx that are easily absorbed by alkaline desulfurizers and water, NO_x and SO₂ can be cooperatively absorbed by the SDA rotary spray process; After the pre-charge technology is used to transform the bag, and the dust charge in the flue gas is conducive to improving the efficiency of dust capture and reducing the filtration resistance, and the dust emission concentration is less than 5 mg/m3.