Abstract: Using conventional observation data, ground intensive observational data, satellite cloud images, microwave radiometer and radar data, a strong hail event in Jiangsu Province on July 15, 2021 is analyzed. The results show that: (1) Before the occurrence of strong hail, the weather condition is controlled by the subtropical high. There are short wave trough and shear activities in the middle and upper reaches of the upstream. The convective activities triggered by the ground convergence line developed in the southern warm region where is conducive to free convection, and continuously obtained the unstable energy in the warm region, which leads to the occurrence of the hail event. (2) Strong hail in midsummer has the characteristics of strong LI value, large CAPE value, low CIN value and high 0 ℃ level height. (3) The convective clouds triggered by the convergence line moved and developed to the warm zone, forming multiple monomer storms and reaching the vigorous stage in the evening. The first triggered convective cloud cluster reaches the southmost. Under the maintenance of the warm and humid unstable airflow in the southwest of the west side of the subtropical high in midsummer, it obtains the most unstable energy and produces the largest hail intensity and widest coverage. (4) The area with combined radar reflectivity higher than 60 dBz and echo top higher than 17 km in multi unit storm is consistent with the place where hail occurs. The vertical structure of the storm shows that the flow field with low-level convergence below 6 km and high-level divergence above 9 km has an obvious suspension structure.