Abstract: The effect of 84 disinfectant on the treatment of phenol-containing wastewater by sequencingbatch reactor ( SBR) process was analyzed,and the concentration threshold of 84 disinfectant was deter-mined. The toxicity mechanism of 84 disinfectant was analyzed based on toxicological characteristicsand changes of extracellular polymeric substances ( EPS) . The results indicated that when the concen-tration of 84 disinfectant was less than 2 mg /L,the addition of 84 disinfectant would improve the activi-ties of dehydrogenase ( DHA) and phenol degrading enzymes and promote the production of ATP. Thecontents of protein ( PN) and polysaccharide ( PS) in EPS decreased with the increase of 84 disinfect-ant concentration. When the concentration of 84 disinfectant was more than 2 mg /L,the activity of re-lated enzymes was decreased,the production of ATP was inhibited,and the contents of reactive oxygenspecies ( ROS) ,lactate dehydrogenase ( LDH) ,PN and PS was increased. Close-