Based on the data developed from various natural waters in the Qinghai Lake area and ostracodeshells present in drill core QH-16A of recent lake-floor sediments,this paper discusses the distribution ofstable isotopes in the modem water body of Qinghai Lake,and the initial isotopic composition of the lakewater has been deduced.Studies of δ;O,δ;C,Mg/Ca and Sr/Ca in ostracode shells provide the basisfor the establishment of the model of climatic fluctuation in the Qinghai Lake area since the postglacial age,as well as for the elucidation of the environmental evolution of the water body of Qinghai Lake since thepostglacial age.