Based on the reanalysis data with 1.0°×1.0° resolution from NCEP/NCAR, the ci rculation background and the main influencing systems of “07.17” torrential ra instorm in the west of Chongqing in 2007 are analyzed. The results indicate that under advantageous largescale circulation background coordination, the main i nfluence systems were the southwest vortex and lowlevel jet stream. The west P acific subtropical high provided the advantageous condition for transport ation of water vapor by its west stretch and north lift. The strong raining processes began at the peak of the development of southwest vortex. The high center and i ntensity of vertical helicity had a corresponding connection with the position a nd intensity of heavy rainfall. Although without surface cold air intrusion, in the upper troposphere the dry air intrusion provided triggering power of rainsto rm. The strong convection weather was affected directly by the dry and cold lid at high level caused by strong cold advection and the warm and wet air at low le vel when they interacted with strong ascending. The different influences of dry intrusion at different levels over the southwest vortex made high potential vort icity in upper troposphere go down and increase in lower troposphere, which stre ngthened southwest vortex and the intensity of precipitation.