Abstract: The regional rainstorm occurring in Yibin on May 31, 2023 was diagnosed and analyzed by using the conventional meteorological observation data, FY4 satellite data, Doppler weather radar and reanalysis data of ERA5. The results showed that: (1) Under the large-scale circulation situation of the subtropical high-pressure southward descent and the eastward movement of the upper trough, the cold air countered the warm and humid air from the South China Sea and the Bay of Bengal in the southern part of the basin, cooperated with the high-level divergence suction, resulting in regional rainstorm. (2) Before the arrival of cold air, the thermal convection was triggered by the ground convergence line to produce warm area rainfall, and the thermal convection occurred on the warm side of the temperature gradient intensive area. As the cold air moved southward, the heavy rainfall was triggered by the cold air and terrain uplift, and the heavy rainfall area advanced from north to south with the cold air. (3) The convergence area of the water vapor flux in the low layer was in good agreement with the heavy rainfall region, which was of great reference significance for the short-term weather forecast.