Abstract: Using hourly rainfall data and ERA5 reanalysis data, the rainfall characteristics and atmospheric circulation anomalies of the persistent rainstorm process in the west of the Basin from August 10 to 18, 2020 were analyzed. The following conclusions are obtained: The continuous rainstorm process showed the characteristics of long rainfall duration, large cumulative rainfall and strong rainfall. Both daily and hourly rainfall showed significant extremes. Heavy rainfall usually occurred in the 40 km range where the terrain rose steeply from 500 m to 2000 m upwind slope. The east and strong South Asian high and the west and strong subtropical high were stable and less active. After being blocked by the eastward migration and southward pressure, the upper trough overlapped with the plateau trough and continued to affect Sichuan, It provided a favorable circulation background for persistent rainstorm. The Bay of Bengal was the main source of moisture, the continuous and extremely strong water vapor supply supported the continuous rainstorm. The atmospheric junction was in convective instability in the early stage of the process, with significant thermal effect. In the late stage of the process, the thermal effect weakened, the southwest vortex developed deeply and the dynamic effect strengthened, The characteristics of vorticity and divergence were stronger than those in the same period of history, and the strong dynamic conditions led to the occurrence of persistent rainstorms.