Considerable long-term variability was found in precipitation changes in western Chi-na,where arid or semi-arid climate predominate.A set of17-site series of proxy precipitation da-ta was applied in this paper,among which11are tree ring series,4are historical data series and2are ice core series.The proxy data were normalized as following:the average of1880～1979was taken as normal,and percentage anomalies were calculated for each decade from the1600s(1600～1609)to the1990s(1990～1999).Finally,EOF analysis was carried out.The EOF1shows great concentration of the variance in Tarim Basin and north of Qilian Mountains.It is in good accordance with the characteristics of EOF1found in precipitation observations and simulations covering1951～1999.It proves to certain extent the reliability of the proxy data.The400-year se-ries of precipitation for western China shows significant dry period in the17th century,especial-ly in the first half of the century.An increasing of precipitation was found in the second half of the20th century,especially during the last30years.These dry period and the increasing of pre-cipitation may associate with the Little Ice Age and Modern Warming separately.Finally,"secular periodicity"was studied.It was manifested well in the deficits of precipitation in early period of each century.