Abstract: In this paper, a process of long drought to heavy rainfall from May 14 to 15, 2023 in Dali Prefecture of Yunnan province is analyzed on basis of conventional observation data, NCEP reanalysis data, satellite cloud images and Doppler weather radar echo charts. The results show that the main weather system giving rise to the heavy rainfall process were the Bay of Bengal storm Mucha and the South Trough in 500 hPa. The coupling effect of upper- and lower-level jet streams enhances vertical updrafts and increases rainfall intensity. After the formation of the storm in the Bay of Bengal, the cloud-top temperature of the storms below −80 ℃. The peripheral cloud systems of the Bay of Bengal storm and its weakened remnant clouds after landfall merged with the southern branch trough cloud systems, then moved northeastward to affect Dali Prefecture, triggering persistent rainfall. During periods of relatively high rainfall intensity, the cloud intensity over Dali Prefecture was not very strong, with cloud-top brightness temperatures ranging from −30 to −20 ℃. During the heavy rainfall west Yunnan area located in water vapor transport with plentiful vapor in the middle-low level. And Dali region was in a ascending motion area through the whole atmosphere with obvious convergence in low level and divergence in upper-level. The region was also controlled by a high energy tongue in 700 hPa. The rainfall process was caused by flocculent mixed type precipitation echoes with the maximal intensity of their rada echoes being 35 dBZ and lower echo top heights. The radial velocity map of radar displayed that the zero velocity line has an S-shaped distribution held for a long time. The presence of long duration of southwest jet and warm advection in middle-low of troposphere was main feature of the wind profile products for the heavy rainfall process.