The Bieletan section is located in western Qarhan Salt Lake, and there are 1.8 bt low assay solid potassium in S4 salt layer. This paper studied mineral identification and the geochemical analysis of seven cores samples from the Bieletan section. The polyhalite is in the presence of two modes: primary orign and penecontemporaneous replacement. Polyhalite mineral shows the phenomenon distributing around the lake, and polyhalite was formd by replacement with gypsum and other sulfate minerals, or even with halite. Studies suggest that the formation of polyhalite related to supplies of magnesium sulfate subtype brine.The polyhalite in the Beletan area reveals the mineral polyhalite commonly occurs in marine evaporite deposits formed by metasomatic replacement brine of land facies lake with early formed saline mineral. Therefore, the origin of polyhalite mineral in the Bieletan area has some indication significance for finding marine potash deposit.