Studies on sulfur isotopes of marine sulfate minerals can indicate the characteristics 〖JP2〗of ancient seawater〖JP〗 at that time, and provide important evidence for material source analysis, stratigraphic correlation and sedimentary environment conditions. Except for a large amount of anhydrite- salt deposits, sulfate- type potassium mineral polyhalite associated with salt, which has been called “a new type of polyhalite potassium ore”, is also developed in the Middle and Lower Triassic marine evaporite strata in northeast Sichuan. Therefore, the study of sulfur isotope in this area can reveal the sedimentary environment and its evolution of the evaporite; at the same time it can also provide evidence for the provenance analysis of potassium salt mineral polyhalite. However, researches on sulfur isotopes in the study area mostly existed in the evolution law of large time scale and global stratigraphic correlation. Studies on the evolution of δ34S in the fourth and fifth member of Jialingjiang formation where polyhalite is developed and its indicative significance are rare. In this paper, a high- precision analysis of δ34S has been carried out using anhydrite, polyhalite and mixed samples of the two above from Well CXD1. It shows that there is no obvious sulfur isotope fractionation between anhydrite and polyhalite. Meanwhile, δ34S results show that the main source of potassium salt mineral polyhalite and its associated anhydrite is seawater, but it is also affected by bacterial sulfate reduction and evaporite mineral precipitation. In addition, the δ34S evolution pattern is obviously consistent with the sequence evolution of the 4th and 5th embers of Jiangling Formation, which indicates the δ34S analysis is of great significance for the analysis of evaporative sulfates sedimentary evolution and the high- precision correlation of the strata in the region. It can be used as an important means of high- resolution correlation and ore layer location in the further exploration of polyhalite- type potassium salt deposits.