Abstract: A novel type of integrated A/O reactor was used to study influence of addition of sulfate on the starting-up of the integration A/O reactor. The results showed that if without addition of sulfate, CODCr removal rate in anaerobic zone was as high as 93%, and CODCr removal rate in aerobic zone was as high as 90%, after 23 days of start-up period. If with addition of sulfate and the CODCr/SO42- was 5:1, CODCr removal rate in anaerobic zone decreased to 90%, and CODCr removal rate in aerobic zone decreased to 80%. At the same time, the system’s pH, alkalinity, ORP, gas production, gas phase component of CH4, CO2 were respectively stably at 8.0-8.5, 1700 mg/L, -445 mV, 2.8 L/d, 27.9% and 52.5%, which showed that the integration A/O reactor had good stability when treating the wastewater contained sulfate.