<p>The total amount of summer extreme precipitation (EP) over the lower reaches of the Yangtze River Basin (LYRB) exhibited a notable transition from a high-value phase in the 1990s (e.g., 1995, 1998, and 1999) to a low-value phase in the 2000s (e.g., 2004, 2006, and 2007). This shift was largely driven by EP days concentrated in June. To investigate the mechanisms behind the shift, daily precipitation from June 1 to 30 during these identified high and low EP years was extracted and subsequently categorized as high precipitation and low precipitation days, respectively. The differences in moisture transport and vertical motion between high and low precipitation days were quantified to identify key drivers from a synoptic-scale perspective. Results show that the dominant moisture sources contributing to the difference come from southern tropical oceans, contributing 57.1–98.9&#xa0;mm on high precipitation days, compared to only 24.7–53.5&#xa0;mm on low days. The mechanisms governing vertical motion difference exhibit asymmetry. On high precipitation days, anomalous ascent was dynamically attributed to the upward gradient of vorticity advection and warm advection anomalies. The upward gradient of vorticity advection anomaly resulted from a meridional dipole over the Tibetan Plateau (TP), induced by quasi-zonal wave trains from Europe, along with warm advection anomaly from a TP warm core. Conversely, anomalous descent on low precipitation days was dynamically driven by the downward gradient of vorticity advection and cold advection anomalies. The downward gradient of vorticity advection anomaly occurred due to a negative geopotential height anomaly over the southeastern coast of China, coupled with cold advection from cold anomaly over the eastern TP slope. This research advances our understanding of the EP variability and provides important insights for predicting EP in the densely populated LYRB region.</p>