Abstract: Based on NCEP/NCAP data sets and dynamical diagnostic, the meridional circulation fact of torrential rain over the mid-lower Yangtze reaches was presented with composite analysis. The downward flow of secondary circulation occurred obviously while deducting the day variety of perpendicular motion. With calculating complete form vorticity equations, the further results show that the negative vorticity is stimulated by diabatic heating over the high layer, which locates at west side of the heating center, and versus east side is positive vorticity. In the low layer there is opposite exactly. Finally, the analysis emphasizes that the subtropical high all will move along the local negative voeticity center for variety direction with South Asia High.