Abstract: From 00:00 (Beijing Time; the same below) to 07:00 on March 3, 2025, a supercell storm in northern Jiangnan experienced multiple episodes of merger and splitting, with a lifespan of 7 hours. Based on surface and upper-air observation data, dual-polarization radar data, and wind profiler radar data, this study processed the radar base data using ROSE 2.1 and PyDDA software, the dual-polarization characteristics and maintenance mechanisms of the storm are analyzed quantitatively in combination with cloud bridges. Finally, the key points for forecasting such storm weather are presented. The results are as follows: (1) A short linear storm existed at the rear of the supercell and continuously extended cloud bridges forward to merge with the supercell. This merging process was characterized by an increase in the horizontal width of the differential reflectivity factor (Z_DR) column and specific differential phase (K_DP) column above the 0 °C level, along with a higher height of the K_DP column. (2) Concurrently with the merger, the supercell split rapidly from top to bottom. After splitting, the southern cell inherited the mesocyclone, and the radius of the mesocyclone decreased significantly; the strong stretching effect led to a sudden increase in upward motion. (3) The tangential merger of small cells at the rear of the supercell (along the storm’s moving direction) significantly enhanced the upward motion on the supercell’s southern side. The cells split from the southern side of the supercell developed rapidly and replaced the original supercell. Such a repeated iterative process of multiple splits and mergers is the main mechanism underlying the supercell’s long lifespan. (4) In operational forecasting, under an environment with strong vertical wind shear, if thunderstorms at the rear of a supercell merge forward with the supercell (accompanied by cloud bridge formation) and the supercell itself splits, special attention should be paid to the possibility of the supercell maintaining for a long duration.