A heavy rain event occurred on 2003-08-25 in the southwestern Shandong Province is simulated with the numerical model MM5V3. The results indicate that the MM5 model simulated the rainstorm and the development of the mesoscale system successfully. The event occurred at the stream convergence area of a low-level jet and east wind circumfluence. The length of the convergence area was about 800 km from west to east. The convergence of warm and cold air induced the strong ascending motion; the lower-level jet was enhanced, transport- ing large quantities of warm, moist air into the system; and east wind circumfluence transported large quantities of cold, moist air into the system. Furthermore, due to the coupling between upper- and lower-level jets and the associated lower convergence and upper strong divergence, the continuously developing mesoscale system resulted in the heavy rain in southwest Shandong Province.