Abstract: To improve the treatment effect of ABR (anaerobic baffled reactor) for low concentration wastewater, the effect of low intensity ultrasound on the treatment of low concentration wastewater was studied by perform- ing a contrast test of ABR in ultrasonic group and control group. The results show that when using the energy density of 0.1 W/mL ultrasonic every 24 h from each compartment of ABR removed 10 % sludge for 10 min of irradiation processing, the average removal rate of COD increased by about 7.2 %. By this irradiation, the total amount of extracellular polymeric in each compartment of ABR is essentially the same, the content of protein is increased, the content of polysaccharides is reduced, the content of DNA changes little, and the particle size of granular sludge is decreased. It is also found that the average COD removal rate of ABR in the ultrasonic group is 8.6 percentage points lower than that in the control group at low temperature, which is only 0.7 per- centage points lower than that in the control group. Under low temperature condition, the strengthening effect of ultrasound is more significant than that of normal temperature袁and the ABR of the ultrasound group is 4 days earlier than the control group to resume stable operation.