A severe drought occurred in SichuanChongqing region in 2006 summer. The high temperature disaster was rapidly weakened by the first rainstorm of autumn and the local drought situation was simultaneously alleviated. However, the strong r ain also caused significant economic loss in many areas. To better understand th e causes of the heavy rain, diagnostic analyses are given by using daily 1°×1 ° grid reanalyzed data from NCEP/NCAR at 00:00(UTC), 06:00, 12:00, and 18:0 0. The findings show that the position of low level jet is different with other process, it appears in the north side of the vortex, which sped the transfer of cold air and water vapor coming from the north. Furthermore, both the appearance and disappearance of low level jet are early to the wind convergence region, wh ich is dynamical condition of the occurrence and development of low pressure. An alysis of apparent heat source and apparent moist sink suggest that cumulus conv ection activities were active, and the convective rainfall dominated.