Fluctuation of closed-lake level is a highly sensitive indicator for climatic changes.It is verified by lake water equilibrium.Its sensitivity can be expressed in the following equation: Z=A_l/A_b=(P_b-E_b)/(E_l-P_l).Closed lakes in the Middle Kunlun Mountains have undergone three high lake-level stages since 17000a B.P., i.e.around 17000a B.P., 12000a B.P.and 8000-6000a B.P.The first high lake-level stage has relevant to ice melting, shift of westerlies, change of soil humidity and solar radiation.The second stage is relatively stable or a gentle rising again in process of lake shrinking.The third stage ig a result of the global wet and warm climate.Theoretical research and case analysis show that fluctuations of closed lake-level not only can indicate the climatic changes in geological time without meteorological records, but also can meet a deficit of meteorological materials for historical time.Moreover, the Middle Kunlun Mountains is a suitable site-for predicting.