Abstract: To study the effect of the organic loading rate on the simultaneous removal of SO₄^2- and NO₃^- and to determine the appropriate range of ρ(COD)/ρ(SO₄^2-), the anaerobic baffled reactor(ABR)was conducted to treat the synthetic sewage with SO₄^2- and NO₃^-. The operational conditions were as follows:the hydraulic retention time (t_HR) was 48 hours, pH value was more than 6, and temperature was controlled at (34±1)°, respectively. The COD concentration of the organic load was gradually enhanced in experimental process. The three stages of the influent COD concentrations were 5 g/L, 6 g/L and 7 g/L, respectively. The experimental results showed that the removal rate of SO₄^2- and NO₃^- of wastewater was not affected with improving the organic loading rate, and the removal rate of SO₄^2- and NO₃^- was up to 96.5% and 97.8% respectively. When the rate of ρ(COD)/ρ(SO₄^2-) was more than 14, the removal rate of SO₄^2- was up to 90%. The distribution of microbial population in each cell of ABR was adjusted according to the influent pollutant concentration. The ability to resisting the impact load of ABR was strong, but the recovery period was longer than 30 days. With the improvement of the organic loading rate, the percentage of methane content was gradually increased from 40% to 90%. With the experimental time of extension, the two physiological groups of the methanogens were in a dominant position and instead of the main methanogens using acetic acid in ABR, which metabolized acetic acid and H₂/CO₂.