The Vientiane Basin of Laos belongs to the secondary basin of Sakon Nakon Basin, where thick layer of potash are deposited, Through the study, it is found that the water- insoluble substances mainly include anhydrite, boracite, muscovite, quartz, hilgardite, carbonate minerals and scattered pyrite. According to the distribution and combination characteristics of water- insoluble minerals in boreholes, it is found that from the precipitation to the end of potash salt, the water- insoluble substances appear regular characteristics: the more potassium salt content, the more boracite content, the less anhydrite, and oolitic boracite appears in the peak period of potassium salt. the regular distribution of oolitic boracite shows the sedimentary environment is a turbulent shallow water environment. The mineral assemblage, morphological characteristics and boron isotope analysis of water- insoluble minerals show that potash deposits are not immutable, but have obvious stages. The process can be divided into four different stages: the stage of potassium salt out, the early stage of potassium salt stage, the middle stage of potassium salt stage, and the later stage of potassium salt stage. The middle stage of potassium salt stage is the peak period of potassium salt deposition. Therefore, the study of water- insoluble matter can be used as an important index for the study of paleopotash mechanism.