By using of the routine sounding, surface observation data and analysis of satellite image, two abrupt rainstorm in Xi’an are analyzed. It shows that the cause of rainstorm is the effect of the easterlies wind jet along the north side of typhoon and the low-system of the westerly belt in the middle latitude, the main vapor and energy pathway is the jet of the easterly belt along the north side of typhoon low- pressure circulation, the meso-β scale convective system (M_βCS) bring on development and maintain of abrupt rainstorm.