According to the high resolution sediment data reveal by a core in deep water area in Qinghai Lake, the fluctuation of lake level in the last 600 years is reconstructed.The results show that the fall of Qinghai Lake level was more than 9m in the first half of 18th century. Moreover, there is a close relationship between lake level and climatic fluctuations in century time scale.The rises and falls of lake level are more or less in line with the wet and dry stages in the last 600 years.Wavelet analysis results indicate that the environment in Qinghai Lake has a quasi 180 year cycle during the research period.