Chapter 7 mainly focuses on the decolorization treatment technology. Firstly, the relevant content of decolorizing coagulation was introduced, and then the types of decolorizing coagulants were expounded, covering inorganic coagulants and organic coagulants. Then, the focus will be on explaining the dicyandiamide formaldehyde condensation polymer, including its decolorization effect and mechanism, as well as its preparation method and production process. It will also be compared with other coagulants. Subsequently, the factors influencing the coagulation and decolorization effect of dicyandiamide formaldehyde condensation polymer were discussed, such as the molecular structure of the dye, the pH value of the dye solution or wastewater, the stirring speed, the dosage of the decolorizing agent, as well as the structure and coagulation mechanism of the decolorizing agent. Finally, the new research progress of coagulation decolorization and other decolorization treatment technologies are introduced.