In the context of high-resolution TBB data, every 6h NCEP/NCAR reanalysis data sets and daily rain data, the mechanisms for the regional torrential rain development over the mid-Yangtze River basins are investigated by means of composite analysis. The results show that the heavy rainfall event often occurs in the area where the upper level diverging flow appears, and heavy rainfall is also related to East Asian Subtropical monsoon surge. Result further indicates that the ageostrophic inertial advection divergence makes the major contribution to the total upper level divergence fields. Due to the role of NW-SE oriented upper tropospheric jet axis, the distribution of horizontal wind field will be inhomogeneous on the jet exit area, and results in strong convergence over the right side of the upper level jet. The incline jet axis and strengthened convergence happen earlier than the rainfall does.