Based on NCEP/NCAR reanalysis data and daily precipitation data from 274 meteorological observation stations in northwest China from 1961 to 2015, the spatial and temporal variations of summer precipitation in northwest China over the past 55 years are analyzed using EOF analysis and accumulative anomaly methods. The conclusion are as follows. 1) The evolution of summer precipitation in Northwest China from 1961 to 2015 can be divided into three periods. The precipitation in this region was generally low from 1961 to 1975; from 1976 to 1996, there was more precipitation in the east of this region and less in the west; however, precipitation in the east was less while it was more in the west from 1997 to 2015. 2) From 1976 to 1996, there was more precipitation in the east of Northwest China because of the obvious increase in summer precipitation intensity and frequency. However, the precipitation in the west was less because of the decrease of the frequency of light rain and moderate rain and weakened intensity of precipitation. From 1997 to 2015, due to the decrease of effective precipitation days and the weak rainfall intensity, the precipitation in the eastern part of Northwest China was lower. At the same time, the precipitation intensity in the western part of Northwest China obviously increased and the number of continuous precipitation days and extreme precipitation events was up, which led to more precipitation in this region. 3) The evolution of midlatitude wave train in the middle troposphere of the northern hemisphere led to the shift of precipitation area, while the water vapor transport from eastern Europe and the Indian monsoon played a key role to abnormal precipitation.