29 representative stations in Northwest China are selected using EOF analysis,and the temporal and spatial characteristics of the interannual and interdecadal variations of 50-year spring and summer precipitation are analyzed.It is found that the tendency of precipitation in northwest China is positive to the west of 103°E longitude and negative to the east.And there are a quasi-three years periodic oscillation of precipitation and a sudden change in the spring precipitation in the middle 1980’s in northwest China.The above results indicate that the wet/dry phase of climate in northwest China is close related with the 500hPa height field and the location and intensity of subtropical high.