Using the Jinan S-band dual-polarization Doppler weather radar data, Zhangqiu sounding and ground conventional meteorological observation data and disaster investigation, this article analyzes the dual-polarization and microphysical structure characteristics of a hail supercell storm that occurred in Zhangqiu, Jinan on 9 July 2021. The results show that under the background of cold vortex weather, strong vertical wind shear and strong convective available potential energy were conducive to the formation and maintenance of supercell. The gust front was the trigger mechanism of the storm and the long-term maintenance mechanism of the storm. The initial storm was triggered by the gust front and it developed into a supercell through merging. In the mature stage, the intersection area between the west side of the storm and the gust front continuously excited new cells, which merged with the main body, thus the storm maintained for a long time. The strong divergence of storm top was one of the key factors for the long-term maintenance of mesocyclone and the high height of storm top. In the super-large hail stage, there existed a clear inflow gap at the right rear of the storm bottom, and there was a differential reflectivity arc in front of it, manifested as a small amount of large liquid particles or small wet ice particles. The strong reflectivity factor area on the left side of the inflow gap corresponded to small differential reflectivity and small correlation coefficient, which was the hail falling area. In terms of the vertical structure, there was a deep bounded weak echo zone on the side of the strong updraft area, and a differential reflectivity ring was distributed below the height of the 0°C layer. There was a differential reflectivity column in the bounded weak echo zone and above it, and the height was higher with a little larger liquid or melting small ice particles. The higher differential reflectivity column indicates that the updraft in the storm is strong and high, which is benefitical to the development and maintenance of the storm and the wet growth of hail particles.