The environmental problem caused by industrial emissions of NO x has been studied in the past dacades. In this study, red mud coupling with phosphorus sludge were used to enhance the solution to absorb NO x from the flue gas. Firstly, red mud reacted with the binder silicic acid in the phosphorus sludge, destroying the emulsion structure of the phosphorus sludge. Then, the P 4 in the phosphorus sludge is completely released, and the P 4 reacted with O 2 in the flue gas to produce O 3 and O. NO and NO 2 contained in the flue gas reacted with the active O and O 3 to produce high-valent NO x , such as NO 3 , N 2 O 5 . At last, the mixed slurry of red mud and phosphorus sludge absorbed the high-valent NO x , resulting in the formation of Ca 5 (PO 4 ) 3 F along with HNO 3 . Using phosphorus sludge to produce O 3 in the reaction process can reduce the production cost of O 3 and achieve waste utilization. Meanwhile, the interaction between red mud and phosphorus sludge can promote phosphorus sludge to produce O 3 and remove F - from phosphorus sludge, as well as avoid the problem of secondary pollution. This study should be helpful for red mud and phosphorus sludge utilization and flue gas denitration.