Abstract: The regional severe precipitation occurred in Guizhou in mid July of 2012. We divided the rainfall process into two stages and compared them by diagnostic analysis in terms of impacts system and formation mechanisms, using the NCEP/NCAR 1o×1oreanalysis data by 6 hours, the conventional meteorological data and surface observation data encryption. The results show that: the first stage belongs to the convective precipitation and the influencing systems mainly contain upper trough, middle and low level shear lines and low-level jet. The surface convergence line is the dominant factor of the first stage strong rainfall. The second stage is mainly affected by the altitude system (upper trough and low vortex) influence, and belongs to both convective and stable precipitation. The water vapor flux convergence center and strength can well indicate strong precipitation drop zone. Atmospheric instability is more likely to cause short- time severe convective weather. The configuration of middle and low level cyclonic vorticity and upper level anticyclonic vorticity is more conducive to the strong precipitation.