Abstract: The data from 10 lake areas can be summerized as follows: 1. Mineral assemblage is mainly illite( relative amount 80-90%), then chlorite ( relative amount 10-20% ) and little montmorillonite. 2. Chemical composition of clay minerals is characterized by rick K and Mg. In general, chemical composition is similar to the continent clay of cold-warm zone in the nonsalt　formation stagel but similar to salt-bearing clay in the salt-formation stage. 3. Clay minerals are generally allothigenous, but some minerals present the transformation. The clay mineral assemblage in salt lake is like that in the soil around he lake. However, Table land Fig. 1 show that there are two kinds of chlorite in the different stages of salt lake formation. It is velieved that Mg-Fe-chlorite may be formed in the sedimentary process of the salt lake. 4. Based on the data concerned, it is considered that the climate has been getting drier and drier from ancient timea to the present. Chlorite is a significant facies indicator in the evolutionary process of salt lake.