An extreme rainstorm has occurred in the midwestern of Gansu Corridor arid zone on 4-5 June 2012. Using the data of conventional and automatic weather stations, FY-2D satellite cloud image as well as NCEP 1°*1° reanalysis data, the impacts of influence system configuration, meso-scale characteristics, water vapor transport and unstable energy have been analyzed. The main results are as follows. After the ground cold front had passed, rainstorm happened, cooling condensation effect was significant. No convergence system formed on ground, while strong suction existed in upper troposphere; plateau low vortex which was blocked by its downstream weak ridge stayed longer over the rainstorm area in middle troposphere; a shear line could be found in low troposphere, the configuration of the upper and low influence systems provided meso-scale convection conditions. Water vapor came from east and west in the low troposphere and south in the upper troposphere, the west vapor transport was strongest, and east vapor transport was affected significantly by high pressure. The whole precipitation water was twice more than the climate. Cooling and humidifying in the boundary layer forced the convective energy to be unstable, and free convection altitudes was low, without the need of strong uplift triggering mechanism. The six meso-beta-scale convection cells had been activated at the cold air intrusion of low vortex cloud, and Yumen station which was affected by four convection cells was divided into two periods to produce short-time severe precipitation.