Abstract: A town sewage treatment plant in Chongqing was studied, and it was found that the sewage treatment plant sludge index (SVI) was between 262-380 mL/g and at the sludge bulking state. Low dissolved oxygen and low sludge load were the main reasons of sludge bulking in the sewage treatment plant. Micro bulking of activated sludge in a certain extent could not only guarantee the stable discharge of COD_Cr, ammonia nitrogen, SS, TP and other indicators in the effluent, but also be conducive to the energy saving of the sewage treatment plant.