There are undersand salt lakes around Qarhan Salt Lake of Qaidam Basin. Their brine chemical compositions are obviously different from those of surface flows and open salt lakes, with higher Na⁺+C^-, lower Mg²⁺+Ca²⁺+SO₄^2-, poor K⁺+CO₃^2-+HCO₃^- etc.. Salt-forming beds of undersand salt lakes contain neogenic minerals with detrital minerals carried, of which salt mineral assemblage is:halite + koenenite + carnallite. The facial map of isothermal evaporation at 251 indicates that the evolution direction of their brine tends to immigrate to carnallite area. When their brine passes through the channel of covering strata, physical and chemical affection may occur, and special sedimentary characteristics be observed. Ail these indicative characteristics may provide evidences for further exploitation of iindersand salt lakes.