Abstract: To determine the sulfate, sulfite and thiosulfate concentrations in sewage sample, this study firstly developed a pretreatment method to separate sulfite and sulfate by acidification and nitrogen purge. The test results validate that, sulfite can be effectively removed by 3.0 L/h nitrogen purge for 15 minutes when pH is adjusted 1.61. Then, analyzing the pretreated and un-pretreated samples by ion chromatographer, sulfite and sulfate concentrations can be determined by calculation. The anti-oxidation effect of Sulfur anti-oxidation buffer (SAOB) for sulfite is also tested and validated. Finally, this pretreatment and analysis method for determination of sulfate, sulfite and thiosulfate by ion chromatographer was developed and tested by synthetic sulfur-containing wastewater. The results validate that the method works.