Chemical coagulation+biochemical treatment, in the pretreatment process, the paper-making black water decolorant is used to make the color of water clear. The decolorizer mentioned here is a kind of flocculation method, which makes colloidal suspended pollutants in wastewater in a fine state through flocculation, electric neutralization, bridging and netting. It is difficult to settle, the filtered pollutants are condensed, and the flocs are integrated into larger particles, which are separated from the wastewater to realize decolorization and purification of the wastewater.