〖WT5HZ〗Abstract:〖WT〗Based on the NCEP final analysis data,a mesoscale modelWRF was used to simulate a heavy rain process,which occurred in Jiangsu Province during 22—23 July 2008.The results show that the WRF has a strong simulating ability for precipitation as well as has a good capacity to predict the mesoscale weather systems.In this rainfall event,the rational allocation of lowerlevel wind shear,cold air and upper air jet stream strengthened the development of vertical circulations,which inspired the convection development in the rainfall region.Also,the upper air convergence and lowerlevel divergence in the large scale flow filed are favorable for the rainfall occurrence,where the strongest water vapor transfer from 850 hPa is necessary.On the basis of energy analysis,not only a high Kindex value all over the Jiangsu Province,but also substantial energy accumulation in the north and middle of Jiangsu provides the instability condition for the precipitation.In addition,the coupling of helicity with a negative(positive) value at upper(lower) levels is the dynamical mechanism to activize and maintain such a low pressure torrential rainfall.