Abstract: NCEP/NCAR1 °×1 ° reanalysis data and MICAPS real-time observational data are applied to diagnose the rainstorm occurred in August 2nd to 4th,2009 in the Chongqing area caused by Southwest Vortex.Comprehensive analysis of new diagnostic physical quantities,such as: vertical flux of water vapor divergence and wet helicity,show the water vapor accumulate at 850hPa,and accompanied by the increased ascending vertical velocity.The water vapor rising convergence is consistent with precipitation of greater value in the same area.The horizontal distribution of negative wet z-helicity at 500 hPa correspond well with the heavy rainfall center of the same period of time.In the vertical distribution of the rainfall area,the favorable dynamic structure of the positive vorticity with water vapour convergence rotation in the low-level and negative vorticity with moisture divergence rotation in the high-level contribute to trigger the heavy rain.