With EOF and ROEF and wavelet analysis,the abnormal characteristics and the evolution rule in Northwest China are studied on the basis of the precipitation and temperature data of June-September for the period 1961-2000 collected from 168 stations. The results show:(1) The abnormal characteristics of precipitation in Northwest China is affected by the same large scale synoptic system,the precipitation abnormal area can be divided into seven regions. (2) The changes with time and periods of precipitation at each station are not the same. (3) The trend changes of drought is same at the first and the third region,the others are not the same.