The Qarhan Saline Lake is now in the stage iplaya lakeî, where brine lakes and a dry salt plain coexist. Although an inland lake, it has large amount of marine-type salts. In this lake, there are three different occurrences of potash salts: disseminated, stratoid and layered. Through the investigation of the sediments, hydrological cycles, geochemical processes and geomorphology in and around the lake, and using the specific interaction solubility model, the formation mechanisms of potash salts have been studied and described in this article. It was found that disseminated potash salts precipitate through the slow evaporation of intercrystalline brine. Cooling is an additional factor in the precipitation of the disseminated potash salts. Hydrological cycles are responsible for the accumulation of potassium in brine lakes (e.g., the Dabuxun Lake) seated in the dry salt plain and the formation of stratoid potash along the lake shore. During the playa-lake stage, the shift of inflow river channels may result in the dissolution of dry salt plains and the formation of a brine lake. The sediments, including disseminated potash salts, are redistributed after the dissolution. This is a very important process for the accumulation of potash deposits as discovered in the Dadong Ancient Lake.