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The Ordos Cretaceous Groundwater Basin, located in an arid-semiarid area in northwestern China, is a large-style groundwater basin. SO2-(4) is one of the major harmful components in groundwater. Dissolved SO2-(4) concentrations, and delta 34S-SO2-(4) and delta 18O-SO2-(4) in groundwater from 14 boreholes and in gypsum from aquifer were analyzed. Results show that SO2-(4) in shallow groundwaters originates from precipitation, sulfide oxidation, and dissolution of stratum sulphate, with a big range of delta 34S values, from -10.7 parts per thousand to 9.2 parts per thousand, and addition of SO2-(4) in deep groundwater results from dissolution of stratum sulphate, with bigger delta 34S values, from 7.8 parts per thousand to 18.5 parts per thousand, compared with those in shallow groundwater. This research also indicates that three types of sulphate are present in the strata, and characterized by high delta 34S values and high delta 18O values-style, high delta 34S values and middle delta 18O values-style, middle delta 34S values and low delta 18O values-style, respectively. The delta 34S-SO2-(4) and delta 18O-SO2-(4) in groundwater have a good perspective for application in distinguishing different groundwater systems and determining groundwater circulation and evolution in this area.