Abstract: Based on conventional observation data, automatic station data, NCEP reanalysis data, FY-2G satellite cloud images, and radar data, one continuous heavy rain in the western Meiyu front in Qiannan from 23 to 24 June 2020 was analyzed. Results are as follows: (1) This event occurred under a control of the South Asia High, with the northern boundary of Western Pacific Subtropical High maintaining in the northern South China, the eastward transmission of the shortwave trough and the joint influence of the middle-low shear and Meiyu front. (2) The southwest warm airflow from the Bay of Bengal and the further south airflow from the west of Subtropical High converged in the middle and the east of Guizhou to the Yangtze River. which promoted the establishment of low-level jet flow and provided sufficient water vapor transport for persistent rainstorm weather. (3) The high-altitude divergence, the positive vertical helicity on the south side of the middle-low shear line and the north side of the low-altitude jet provided the dynamic conditions for the rapid development of mesoscale vortex and the condensation of water vapor convergence. (4) The weak cold air southward led by the plateau trough was beneficial to the Meiyu frontogenesist. several γ and β-scale mesoscale convective systems were generated from afternoon to evening. which caused this precipitation process. (5) There was an obvious “train effect” during the heavy rain. The heavy rain was formed in Southern Guizhou due to the continuous convective system .