Objectives: Study the sedimentary environment and sulfate sulfur isotope composition of the Oligocene Series in the Yingxi area, Qaidam Basin, and its geological significance. Methods: The characteristics of main and trace elements, sulfate type, sulfate isotope composition and main controlling factors, the formation mechanism of H2S gas and its transformation effect on reservoirs were carried out. Resultst: ① The average value of Sr/Ba in the study area is 6.71, the average Fe/Mn is 44.35, and the average value of (Fe+Al)/(Ca+Mg) is 0.45, which is the sedimentation of semi- deep lake in salinization; the average value of Sr/Cu is 148.24, which is arid climate; the average value of U/Th is 0.55, the average value of V+Ni+Mn is 495.77 μg/g, the average value of V/(V+Ni) is 0.63, and the average value of Ni/Co is 2.28. The Cu/Zn average value is 1.00, which is an anoxic reduction environment. ② There are many kinds of sulfates in the study area, including CaSO4, Na2SO4 and CaNa2(SO4)2, SrSO4 and BaSO4. Among them, CaSO4 is the most widely distributed, and the average value of sulfur isotope δ34S is 32.23‰, which is obviously heavier than seawater in the same period. It is mainly controlled by a relatively closed sedimentary environment and fractionation of TSR sulfur isotope; ③ TSR generally has a certain improvement effect on reservoir physical properties, although its associated calcite precipitation can occupy a certain amount of storage space. However, the consumption of sulfate can produce a certain amount of secondary pores. More importantly, the product of hydrogen sulfide in the TSR has a strong ability to dissolve, and can enter a very small space where the acidic fluid is difficult to enter. Conclusions:It is proposed that the TSR of the Oligocene in the Yingxi area, Qaidam Basin, is the main controlling factor of the sulfate sulfur isotope composition, and it has a certain improvement effect on the reservoir physical properties.