According to the moist potential vorticity theory, three hailgale events occurred in Guangxi in April 2006 are diagnosed and analyzed in detail. The results show that the convective stability was very small around the area with dense moist potential temperature isopleths; the absolute vorticity increased during the process of cold air moving downward along the isoentrope surface, leading to the increasing of cyclonic vorticity, which is favorable to the occurrence of hail and gale weather. It is found that there is high MPV (moist potential vorticity) descending downward from the upper troposphere before the hail and gale events; and in the areas with dense barotropic MPV isopleths (around the zero line) and around baroclinic MPV negative centers on the 925 hPa level, heavy convection occurs at a higher probability.