Under the background of global warming， summer extreme rainstorm events occurred frequently in Inner Mongolia.As an important ecological security barrier in northern China， the sensitivity of the climate change in this area is increasing.Based on the daily precipitation observation data of National Meteorological Station from 1981 to 2020 and China's first-generation Global Atmospheric Reanalysis product （CRA40）， the variation regularity and dynamic factors of summer extreme rainstorm in Inner Mongolia in the past 40 years were studied.The conclusions are as follows： （1） The spatial distribution of summer precipitation in Inner Mongolia is gradually increasing from west to east， the difference between east and west is obvious， which is closely related to the distribution of the terrain.Hetao area and the southeast of Inner Mongolia are the areas with frequent rainstorm.In the past 40 years， the summer precipitation of most stations in the whole region were decreasing， and the significant decreasing stations of precipitation reached 36.44%.（2） The summer extreme rainstorm in Inner Mongolia mainly occurred in July and August and had obviously interannual variation.The frequency of extreme rainstorm decreased after 2000， but began to increase significantly after 2016.There have been 12 extreme rainstorm processes in the whole region in the past 40 years， which mainly affected the Hetao region in the west and the southeast region of Inner Mongolia.（3）During the extreme rainstorms happened in the Hetao region and the southeast， the large value area of dynamic factor basically coincides with the strong rainfall area， the dynamic factor of the precipitation area in the eastern region is significantly larger than that in the western region.The four dynamic factors had good indicative significance for typical extreme rainstorm process in southeast， but in typical extreme rainstorm process in west， the moist thermodynamic advection factors and the thermodynamic wave activity density performed better.（4） CRA40 reanalysis data showed that during the extreme rainstorm in the western and southeastern regions， the subtropical high was obviously stronger， and 500 hPa was affected by the circulation system with higher east and lower west， obviously water vapor channel was established between them also with significant water vapor convergence.Combined with the remarkable vertical ascending movement and the large value area of generalized potential temperature， meanwhile add the effect of the terrain that both lead to the improvement of precipitation efficiency， the extreme rainstorm events occurred.