Abstract: Based on the determination of trace elements, major elements and clay minerals in the mudstone samples from the Taohaiyingzi section and Lu-D2 well in Jarud area, the Adams's and Couch's paleosalinity formulas are adopted, along with the decision methods of "equivalent boron"by Walker, Sr-Ba ratio, B-Ga ratio and biomarkers, to synthetically analyze the water salinity characteristics corresponding to the sedimentary period of Linxi Formation in Jarud area. The results show that the Linxi Formation at Lu-D2 well formed in brackish-water environment; while that at the Taohaiyingzi section, in freshwater environment. Furthermore, the water salinity appeared the decreasing trend in the sedimentary period of Linxi Formation in Jarud area. To be specific, the lower part strata corresponded to the brackish-water lake environment, while the upper part strata corresponded to the freshwater lake environment. Above all, the brackish-water lake environment could provide the favorable condition for developing thick source rock.