Abstract: Based on ground, radiosonde and radar observation data and ECMWF-ERA5 hourly reanalysis data, a regional heavy rain process in Ya 'an from 29 to 30 August 2020 was analyzed. The results show that the low latitude circulation under the cooperation of typhoon and subtropical high has an important influence on the low-level water vapor transport in this rainstorm weather. The easterly low-level jet at 850hPa triggered the strong convection, and the stable maintenance of the low-level jet transported water vapor and unstable energy for continuous heavy rainfall. The combined effects of the low-level jet and the trumpet topography formed a stable vortex in the eastern Ya'an region and made the mesoscale convective system stable in the region, resulting in the regional heavy rain weather process.