On 21 March 2019, a hail process caused by long-life supercell occurred in Zhejiang Province. In order to study the environmental background and microphysical characteristics of supercell which maintained for a long time, we analyze the evolution of this process by using conventional data, Ningbo S-band dual polarization radar data and hydrometeor classification algorithm. The results show that the high-level trough, 850 hPa shear line and the surface cold front provided suitable background for the supercell. The increase of effective convective potential energy in the storm propagation area, high speed of storm bearing layer, the similarity of the mean wind direction of the storm bearing layer and moving direction of the storm, as well as the eastward propagation of the convective storm along the high pseudo-equivalent potential temperature gradient of surface, and the increase of rotation speed and thickness of mesocyclone produced by the enhancement of strong vertical wind shear in the coastal area, all these factors are the causes of making the convective storm maintain for a long time. Through the analysis of the structure of the hailstorm, the vigorous convection (the maximum reflectivity above 60 dBz, the storm top above 8 km) was found in the whole life cycle, and three obvious fluctuations in the height of storm centroid appeared, corresponding to three hail processes. In this case the vertical integrated liquid water content (VIL) jump increment was lower than the traditional index, but the combination of the vertical integrated liquid water content density (VILD), the maximum VIL and the maximum reflectivity factor could still indicate the hailstorm. The analysis of the dual polarization characteristics, suggest that the tumbling of falling hail resulted in the Zdr close to 0 dB, and the difference between horizontal and vertical polarization waves led to the appearance of large Zdr region at the root of TBSS. The water coated phenomenon made the Zdr value increase and CC value decrease. The polarization parameters Zdr and CC could be used to identify hail in high altitude; Zdr column, near BWER, could not only indicate the ascending motion, but also reveal the different growth stages of hail cell.