The δ¹³C time series obtained from trees in the Tianmu Mountains of Zhejiang Province contain high frequency variations and a long term decrease trend .By removing the long term decrease trend related to the δ¹³C variation with atmospheric CO₂,it is found that the high frequency variation is determined by the precipitation.Relation between the precipitation and the δ¹³C is analysed using PCA in terms of precipitation data in east China.The multiple regression method is employed to reconstruct the historical precipitation in east China,with a view to analyze the climatic change of centuries and evolution trend.