By using NCEP reanalysis data and composition analysis and dynamical diagnosis, this paper compares the difference of the atmospheric circulation features about the typical Meiyu patterns of southern flood (drought) and northern drought (flood), and investigate the performance of dynamic identification of nearly 20 kinds of physical quantities for the main rain belt. The results show that: for the typical Meiyu pattern of southern flood (drought) and northern drought (flood) the polar vortex is stronger (weaker), the amplitudes of roughs and ridges in the middle-highlatitudes of Asia－Europe are larger (smaller), the geopotential height in the middle latitudes during 110°E－150°E is lower obviously, the above differences indicate the power of cold air is stronger (weaker); correspondingly the east part of main body of the South Asia high is more southward (northward); the main body of the western Pacific Ocean subtropical high is more eastward (westward) and its western ridge line is more southward (northward); the Indian monsoon trough is weaker (stronger); both the upper divergence and the lower convergence over the Changjiang－Huaihe River valley caused by the upper and lower level jets are weaker (stronger); the water vapor transport flux over the Changjiang－Huaihe River valley is smaller (larger) which is mainly originated from the southwestern monsoon current (from the southwestern monsoon current and the easterly current on the south side of the western Pacific Ocean subtropical high). It is in good agreement with the main rain belt, such as the strong gradient convergence region of meridional wind on the left side of the low level jet axis, the center of vertical ascending motion at 500 hPa, the high value band of total transfiguration at 925 hPa and 300 hPa, the strong gradient convergence region of meridional vapor flux in the lower atmosphere, the convergence center of Q vector in the middle atmosphere.