Using FNL 1o×1oreanalysis data, FY-2F satellite TBB data and conventional meteorological observation data, the process of a rare autumn rainstorm that occurred in Anshun, Guizhou during the night from September 13 to 14, 2020 was analyzed. The results show that the eastward retreat of subtropical high leads the eastward movement of short-wave trough and the southward pressure of low vortex with shear line, which provides favorable synoptic scale background conditions for the occurrence of heavy rain. The strong water vapor convergence center remained stable in Anshun, and the rainstorm center corresponded to the water vapor convergence center. The superposition of warm advection in the lower layer and cold advection in the middle layer in the rainstorm area is beneficial to the development of ascending motion and provides favorable conditions for the release of energy and latent heat. The mesoscale convective cloud developed rapidly in the generation stage, weakened in intensity and moved slowly after maturity, and moved steadily and rarely over Anshun, which was the main reason for the occurrence of rainstorm to extremely heavy rainstorm in the whole city, and the rainstorm area corresponded well to the area with TBB≤55℃. On the one hand, the atmospheric water vapor, energy and uplift conditions are good where the convective cloud cluster is generated. On the other hand, in the area affected by the eastward movement of the convective cloud cluster, the atmospheric stratification is unstable and the wet layer is deep, but the energy conditions are poor. Therefore, the convective property of the rainstorm process is not very strong, and the hourly rainfall intensity is mostly between 20 and 40 Mm per hour during the period of strongest rainfall.