The characteristics of a supercell hailstorm event, which occurred in the south of Hebei from Laiyuan to Dongguang on June 25, 2020, are analyzed according to the environmental conditions and the wind field retrieval from dual Doppler radar. The results suggest that: (1) This supercell hailstorm was triggered and continuously strengthened in a horizontal convective roll. (2) The possible reasons for the long-life event include that the supercell was in the environment of vertical wind shear, which caused by the medium to strong basic clockwise rotating background wind; the maintenance time of mesocyclone was more than three hours; and there was a strong cold pool. (3) The VIL values of supercells from 55 to 80 kg m^-2 lasted for seven hours, which was consistent with the hail path during the period. The three-body scattering spike or sidelobe echo characteristics appeared for more than four hours, which was consistent with the time of large hail confirmed by the meteorological observation and the disaster investigation in the events and had obvious indicative significance for large hail. (4) There were supercell characteristics such as the hook echo at the low levels, echo suspension, dome structure, divergence in the top of the storm, the column of ZDR and KDP, and so on. The reflectivity over the dome was more than 65 dBz. The wind field was mainly vertical upward but weak horizontal component, which formed a structure of cave-channel and zero-region and was conductive to the growth of large hails. The vertical velocity of the supercell increased with height, which was beneficial to the formation and maintenance of mesocyclone.