Abstract: Using automatic weather station precipitation data, FY-4A satellite data, Doppler radar data, and ECMWF-ERA5 reanalysis data, a mesoscale weather analysis and water vapor source tracking of a rainstorm event in Meishan City from July 11 to 13, 2023 were conducted, and the role of the southwest vortex in this rainstorm was investigated. The results show that: (1) The heavy rainfall occurred under a blocking circulation with high pressure in the east and low pressure in the west. The first stage of precipitation was warm-sector precipitation, triggered by a shear line and topography. In the second stage, the low-level vortex was the direct influencing system. The southwest vortex formed through the intersection of northerly cold air and southerly airflow, gradually developing into a deep system with significant rotation and convergence characteristics. The dynamic enhancement, along with a high-energy and high-humidity area in the lower troposphere, enabled the occurrence and maintenance of the rainstorm. (2) High values of radar reflectivity factor and the low values of cloud-top blackbody temperature corresponded to precipitation intensification, while the opposite corresponded to a decrease in precipitation, showing certain predictive significance. (3) Water vapor tracking results indicate that the main sources of water vapor for the rainstorm were the Bay of Bengal and the South China Sea, with strong convergence occurring over Meishan.