The salt basin of north Shannxi province (Shanbei) during the middle Ordovician was located in the junction of the North China Sea and the Qilian Sea, where developed a huge thickness of evaporite- carbonate sediments. The fifth Member (M5) of the Majiagou Formation is lithologically characterized by mediumand thinlayered muddy or fine grained dolomite and anhydrite, medium- thick layered coarse- grained dolomite and limestone, medium- thick layers halite and anhydrite, and anhydrite and halite with mudstone. In this paper, we carried out a systematic analysis of sulfur isotope compositions for anhydrite from the M5 evaporite- carbonate layers. The study shows that the sulfur isotope values of the M5 anhydrite in the Shanbei salt basin are generally high, ranging from 25.03‰ to 29.25‰, and fall within the sulfur isotope area of Ordovician global seawater spectrum. And sulfur isotope values are closely related to the sedimentary lithology, with limestone/dolomite section (average value is 27.28‰; 25.77‰～29.25‰) >mudstone section (average value is 26.22‰; 25.49‰～28.08‰) >rock salt section (average value is 25.41‰; 25.03‰～26.04‰). Many factors resulted in isotopic differences of anhydrite in evaporite basins. In the study area, high δ34 S values during transgression phases were affected mainly by marine sedimentation, paleoclimate, MSR function under the anoxic condition and others; relatively low δ34S values during regression phases were influenced by the formation of the closed cycle of brine and the addition of the mixed brine formed by dissolving in situ sulfate minerals.