Abstract:Based on the reanalysis data of NCEP and the regular meteorological observation, the large scale background of persistent torrential rain on June 11—13, 2008 in south China is analyzed ,the large scale background environment has been simulated by high resolution MM5 model. The result shows that: (1) Southwest vortex was the direct impact system of the persistent torrential rain, as the vortex move eastward, the torrential rain moved from northern area of Guangxi to southeast area of Guangdong. (2) The stable circulation of two troughs and one ridge at middle and high latitudes, the more southward position of the subtropical high in the west Pacific and small-scale cold current continuously advancing south provided a favorable circulation cold air background condition of middle and high latitude area for the maintenance of the persistent torrential rain. Anomalously southern summer monsoon in East Asia and anomalously strong air current across equator provided abundant moisture for the maintenance of the persistent torrential rain. (3) The result of the simulation proves the large scale circulation background of the torrential rain, and three positive vorticities appeared on 700 hPa are the dynamical factor of the torrential rain.