In view of a rainstorm that occurred in the northeast of Sichuan Basin on 8 August 2021，this paper uses ground observation and reanalysis data，combined with WRF （Weather Research and Forecasting） sensitivity numerical experiments，to study the influence and mechanism of the eastern Qinghai⁃Xizang Plateau topography on this rainstorm process. The results show that during the rainstorm，the Sichuan Basin was mainly affected by the 500 hPa high ridge. The southwest airflow formed by the flow around the southeast side of the Qinghai⁃Xizang Plateau transported warm and humid air to the rainstorm area，and formed a vortex in the basin. The coupling of high and low altitude systems makes the air flow converge and rise，providing good conditions for rainstorm. When the terrain height in the eastern Qinghai⁃Xizang Plateau decreases，the blocking effect of the terrain on the airflow weakens，and the southwest airflow generated by the flow around the southeast side of the plateau weakens and becomes a westerly airflow. At the same time，the northwest air flow on the northeast side of the plateau strengthened and moved southward，further weakening the southerly wind component and water vapor transport in the Sichuan Basin，which eventually led to the accumulation of water vapor on the southeast side of the Sichuan Basin and the southward movement of the rainstorm area.

Keywords： Sichuan Basin ; topographic action ; strong convection ; numerical simulation