The historical climatic data sequence is reconstructed on the basis of tree ring data of Qinghai Lake Basin and neighbouring areas.In this paper four main periods (cold,warm,dry and wet) of the lake basin in the past 600 years are given and the climatic trend is predicted.It appears that the lake water-level falling is mainly caused by the warm-dry climatic tendency in recent 100 years.In addition.the relationships between the annual variation of the lake water level, the weather systems affecting antecedent precipitation.various climatic patterns and land surface meteorological elements are analyzed by means of statistical method.