Because of characteristics of summer rainstorm easy to form disasters,difficultly to forecast,so it has been the focus of the study. Gansu province is located in the upper reaches of the Yellow River,the region at the confluence of the Loess Plateau,the Inner Mongolia Plateau and the Qinghai-Tibet Plateau. Climate type variety are complex,special geographic location and significant spatial variation of precipitation make forecast exceedingly difficult in Gansu province. Previous studies are mostly for the heavy rainstorm,rarely studied the characteristics of the rainstorm days change,but the rainstorm days is also an important indicator of climatic characteristics of heavy storm days in Gansu province. In order to study climate change characteristics and laws of the rainstorm, improve the accuracy of the rainstorm forecast,using daily precipitation data at 80 stations in Gansu Province, NCEP /NCAR reanalysis datasets during 1974-2013,and following empirical orthogonal function,system clustering and composite analysis method,the spatial and temporal variation characteristics of rainstorm days during summer in Gansu province and their relationships with the atmospheric were studied. The results showed that: Rainstorm days in Gansu province experienced three significant interdecadal variation process in recent 40 years during summer around 1989、2002、2009. According to the EOF and cluster analysis,the summer rainstorm days were divided into four distribution patterns,namely the Hedong strong and Hexi weak pattern,Gansu mountain of Minxian pattern,Longnan and Longdong pattern,the whole province pattern. The summer rainstorm days were closely related to the East Asian summer monsoon in the South China Sea with more available moisture. The Hedong strong and Hexi weak pattern and Longdong and Longnan pattern were related to the movement of cold wave. The Hedong strong and Hexi weak pattern corresponded to strengthen with cold vortex of Lake Baikal, cold air south,the monsoon with its position by northwest,moisture from the South China Sea and the East China sea transporting to east. The Gansu mountain of Minxian pattern pattern corresponded to the monsoon with its position by north,moisture from the South China Sea and the Bengal bay transporting to west and meeting in Gannan region. The Longdong and Longnan pattern corresponded to Iran high and Mongolia low weaken,cold air activity reducing,the monsoon with its position by south,moisture from the South China Sea transporting to southeast,cold air backflow more likely to resulted in forming precipitation in Longdong and Longnan region. The whole province pattern corresponded to the monsoon with its position by the Tibetan plateau,moisture from the South China Sea and the Bohai Sea transporting to westwards extending and northwards advancing that impacting most regions of Gansu Province.