The meso-scale synoptic system is successfully simulated with a meso-scale heavy rain numerical model, that leads to heavy rain in the middle valleys of the Changjiang River on 22, July in 2003. Combining surface intensive observations, conventional data and model output products, the meso-scale synoptic system is analyzed particularly. Results show as follows. The heavy rain taking place in the west side of Dabie Mountain is caused by β-scale cyclone on α-scale shear, and the heavy rain near the boundary area between Hunan and Hubei provinces is caused by cyclonic wind perturbation. The positive vortex advection in the foreside of upper trough provides triggering mechanism for the formation of mesoscale heavy rain system. The pressure in the middle-lower troposphere drops under the effect of the positive vortex advection, which generates allobaric wind convergence and then leads to ascending motion. The lift-up of warm and humid air current in the lower troposphere triggers the bursting-out of instable convective energy, which leads to form local convection and heavy rain.