Based on conventional observation data，NCEP reanalysis data，satellite images and radar mosaic products，and combined with WRF mesoscale simulation，the severe convective weather which occurred in the south of Shanxi on 22 May，2013 was analyzed． The results show that during this weather process，lasting transport of positive vorticity advection over Hetao area played a significant role in formation，maintenance and development of the cut － off vortex on 500 hPa level． Both the low － level cold advection from the front and more stronger warm advection from the back made the vortex develop continually，and excited isolated cloud clusters nearby． The vertical structure with high － level divergence and low － level convergence above the cloud clusters made the upward motion strengthen continuously． Consequently，the isolated cloud clusters maintained and developed． These meso － and meso － scale clusters were the direct cause leading to this severe convective weather． The dry frontogenesis caused by surface continuous strengthening of water vapor from the sea at the back of high pressure system and the invading of dry air at the front of ridge，was an important triggering mechanism of the strong convective weather． From the radar mosaic products of composite reflectivity，this process resulted from the development and merging of convective cells． The evolution of these cells went through a process from convective cell，merging，ribbon echo，bow echo to weakening and vanishing ，and the whole process was divided into two stages，when the area，intensity and moving speed of echoes were different，the characteristics of convective weather were different too． Obvious differences among three types during this process existed in temperature and humidity profiles and environmental parameters，which could be served as judging the severe convective weathers．