Abstract: Combinations of statistical analysesincluding principal component analysis, and singular spectrum analyses, were carried out the evolution of trend and interannual oscillatory of precipitation over N W China.From the beginning of 1960s to the initial of 1970s, the monthly precipitation appeared a downward trend; From the initial of 1970s to the initial of 1980s, the monthly precipitation appeared an upward trend ; The monthly precipitation was much in 1980s and less in 1990s.This trend was the strongest in the south of Gansu province and the south and middle of Shanxi province, was stronger in the north of Tianshan ridge.On the interannual timescales, signals of quasi-8.5a oscillation, 3-4a oscillation and quasi-5.1a oscillation whose importance were weakened in turn were found in the space-time-dependent precipitation series.The amplitude of quasi-8.5a oscillation was stronger than one of any of the other two oscillations.On any of the three oscillations, the dist ribution of phase wasn't completely same in space.