Qinghai Lake is the biggest brackish lake of China.It lies in the northeast of the Tibet Plateau.That the location of the lake is influenced by the East monsoon,Siberian-Mongolian monsoon and the Westerlies enables its deposits record the climatic and environmental change sensitively. Based on the analyses of environmental proxies (magnetic susceptibility,carbonate content,TOC etc.),we reconstructed the environment change of Qinghai Lake in the past 900 years Itis indicated reliably by the results that this area has undergone five periods of warm and dry as well as five periods of wet and cold during the past 900 years.The existence of Mediaeval Warm Age Little Ice Age are obvious and the temperature has been rising since the 20th century.Human activity from the 1950's was reflected by magnetic susceptibility clearly.