Abstract: Based on multiple sources of data, from the aspects of circulation background, environmental conditions, low-vortex evolution, and model evaluation, the causes of an extreme rainstorm event in Hunan Province occurred from June 16 to 25, 2023 (hereinafter referred to as the “Dragon Boat Festival Rainfall” event) was discussed. Correction analysis was also conducted on forecast deviations. The results show that: (1) The “'Dragon Boat Festival Rainfall” event had significant convective and mobile characteristics, with daily precipitation at multiple stations reaching historical extremes. (2) The key synoptic cause was the persistent influence of multiple mesoscale convective systems, which were fueled by the eastward movement of a ladder trough and a long-maintained, active low-level vortex. The mesoscale convective systems continually initiated, merged, and developed along the eastern segment of the shear line, forming quasi-linear convective systems that persistently affected Hunan. (3) The convergence of two moisture channels from the Bay of Bengal and the South China Sea, which transported moisture to the southern part of the low vortex, combined with substantial near-surface moisture convergence, provided crucial moisture conditions for the extreme precipitation. (4) The dynamic configuration of “negative vorticity in the upper layer and positive vorticity in the lower layer” contributed to the intensification of the low vortex and enhanced convergence-driven upward motion, representing one of the primary dynamic causes. (5) During the initial warm-sector rainfall stage, numerical models substantially overestimated precipitation intensity. However, as the dominant pattern shifted to low-vortex-driven rainfall, effective forecast corrections could be achieved by considering factors such as the duration of the low vortex and enhanced moisture-dynamic conditions.