A severe hail event occurred along Yangtze River in Jiangsu on 28 April 2015. Based on the data of AWS observation, geostationary satellite, Doppler weather radar and wind profiler radar, this paper analyzes the characteristics of the synoptic weather pattern, thermodynamic conditions, changes of ambient wind field before hailstorm, and structure of the supercell storms. The results show that first, with Northeast vortex and the dry and cold airflow at the back of vortex trough, unstable stratification is formed by the dry and cold airflow in the midhigh level and the warm and humid airflow in the low level, the configuration of the high and low level jet and the surface convergence system provide a favorable thermal condition. The high CAPE values, inversion layer, favorable water vapor in the low layer and the strong deep vertical wind shear are conducive to the occurrence of severe hail weather. Second, the vertical distribution of physical quantity fields, such as average divergence, the mean vertical velocity, relative storm helicity, vertical wind shear, retrieved by the Doppler weather radar and the wind profiler radar data can reflect the rapid change of the ambient field, which is gradually adjusted into the pattern of lowlevel convergence and upperlevel divergence, and the values of the helicity and vertical wind shear are gradually increased before the convective system moves into the area of the radar station. Such situation indicates that the ambient field is suitable for the maintenance and development of the severe convective system. Third, besides the TBSS phenomena and the front inflow notch found in the radar echo of the severe hail supercell, the prominent bounded weak echo area and suspended high strong echo area are made by the persistent deep mesocyclone. The inner loop structure of the supercell is revealed by the application of the dualDoppler radar wind field retrieval technique. The ambient field is cyclonic rotation in the low level while rotation in the middle level is strengthened and the wind field in the high level is diverged. The emergence and maintenance of the vortex in the supercell contribute to the growth of large hail in the air.