In order to solve excessive NOx emission of the grate-rotary kiln flue gas from a 600000 tons oxidized pelletizing production line, SNCR + hydrogen peroxide oxidation denitration was used to upgrade the process and realize the ultra-low emission of flue gas. The treatment capacity of the flue gas in this project was 400000 m3/h. The total investment of the denitration system was about 1.8 million, and the annual operating cost was 1.8946 million.The operation results showed that the concentration of NOx was reduced from 100 mg/Nm3 to 45 mg/Nm3, which was lower than the NOx emission limit (50mg/Nm3) of Shandong provincial local standard (DB 37/990—2019) and realize the ultra-low NOx emission.