Local heavy rainfall occurred over the Qinling and Bashan mountainous area is one of typical meteorological disasters in the eastern Tibetan Plateau. According to the data from routine meteorological observation, the analysis of the heavy rainfall process from 1 to 10 July 2005 in the Qinling and Bashan mountainous area is conducted with the emphasis on the localarea heavy rainfall at the night of 8 July 2005. Using the new generation mesoscale model of the Weather Research and Forecast (WRFV2.1) model, the a mesoscale numerical simulation of the heavy storm rainfall during 8 July 2005 is carried out. It is found that the continuous rainy weather occurred in the favorable background：the existence of relatively stable subtropical high. The simulation results show that a mesoscale lowlevel jet can enhance and accelerate the occurrence and development of mesoscale systems; the convergence at low levels and divergence at higher levels are the dynamical conditions of rainfall systems.