The Weil Sezhong 6 core from Sebei Gas Field in the three-lake area in East Qaidam Basin contains 870m-long section of continuous lacustrine deposits during Early Pleistocene. The characteristics of varved sediments in the part of deep lacus have been recognized by observations of the core. Varved sediments are thinly laminated and made up of alternately dark clay and light silty layers of average 0.75mm thick. The varves could be subdivided into three kinds of couplets:1) silt-clay couplets; 2) organism-bearing clay and silt couplets; 3) marl layer and silty intraclastic couplets. Data of size analysis can be interpreted as the results of suspension setting in deep lake for both coarser silty layer and clayey layer of varves. δ¹⁸O and δ¹³C of the different types of varved sediments show that lake water in Early Pleistocene was of relatively high salinity and seasonally stratified. Varved sediments were deposited in lake transgression sequence related to the regional subsidence of the basin. The depositional sequences of varved sediments could be classified into stable and fluctuated lake level sequences according to the associations of microfacies. Therefore, it can be concluded that the varves axe nonglaciaJ clastic, differing remarkably from glacial varves. The genesis of the varves is further discussed. The deposition of the varves depends mainly upon annually seasonal stratified water column and influx forms, both of which have been controlled by tectonic subsidence of the basin and climatic changes. Carbonates in the varves are considered to be genetically related to arid climate condition during Eariy Pleistocence in this area. Finally, the varved sediments play an important part in environmental reconstruction, i. e.:1) depth of the lake water; 2) changes of supply amount; 3) fluctuation of lake levels; 4) changes of paleoclimates.