Abstract: Based on precipitation data of Xi'an from 1951 to 1995,changes of the precipitation over last 55 years in Xi'an City were analyzed,by using methods of linear regression,moving average,wavelet analysis and M-K mutation analysis.The results showed that the precipitation generally experienced fluctuation process in Xi'an over last 55 years.The precipitation changes in Xi'an were accorded with the precipitation changes in the eastern parts of the Northwest China under the impacts of the atmospheric circulation.The precipitation decreased in spring,summer and autumn,while it had an increasing trend with the fluctuations in winter.The precipitation in autumn had a certain relationship with the El Nino and the La Nina.A significant increasing trend of the precipitation in winter was greatly related to the enhanced west force and increased water vapor from south.The period of the precipitation change with steady periodic surge was three years and six years over last 55 years.The mutation analysis showed that the precipitation in Xi'an both in 1960's and 1990's had a significant mutation point,where it was into less rain period from more rain period.

Key words: Precipitation change, Precipitation change, Wavelet analysis, Mutation analysis