A severe local heavy rain occurred in the southern Shandong Province on 2 September 2004 was simulated by use of the next generation mesoscale nonhydrostatic model WRF. The causes of the heavy rain are analyzed with the reasonable simulation results. The results show that the highhumidity area in the inverted trough of a typhoon is vapor sources. The mesoscale convergence line in the lower stratosphere played a very important role. The smallscale vortex near the front is the direct cause of the heavy rain. Terrain is a trigger mechanism and the interaction between typhoon inverted trough and front enhanced the precipitation.