The effect of 84 disinfectant on the treatment of phenol-containing wastewater by sequencing batch reactor (SBR) process was analyzed, and the concentration threshold of 84 disinfectant was determined. The toxicity mechanism of 84 disinfectant was analyzed based on toxicological characteristics and changes of extracellular polymeric substances (EPS). The results indicated that when the concentration of 84 disinfectant was less than 2 mg /L, the addition of 84 disinfectant would improve the activities of dehydrogenase (DHA) and phenol degrading enzymes and promote the production of ATP. The contents of protein (PN) and polysaccharide (PS) in EPS decreased with the increase of 84 disinfectant concentration. When the concentration of 84 disinfectant was more than 2 mg /L, the activity of related enzymes was decreased, the production of ATP was inhibited, and the contents of reactive oxygen species (ROS), lactate dehydrogenase (LDH), PN and PS was increased.