A widerange disastrous supercell hailstorm occurred in Zhejiang Province on 21 March 2019 is simulated by using the highresolution mesoscale WRF model. Combined with Doppler radar detection products, the characteristics of radar echo structure, flow field structure, hydrometeors and their evolutions are analyzed, and the physical mechanism of hail formation is explored. The results show that the hailstorm occurred and developed in the area where the right side of the highlevel jet axis overlapped with the lowlevel shear line. Strong vertical wind shear contributes to its maintenance and development. The supercell hailstorm exhibits typical characteristics of hook echo, longlasting deep mesocyclone, strong hanging echo, bounded weak echo area, and strong threebody scattering on radar echoes. The simulation experiment successfully simulated the horizontal evolution and vertical structure of the hailstorm clouds. Suitable layer heights of 0 ℃ and -20 ℃， as well as an appropriate thickness of the 0 ℃ to -20 ℃ layer, are conducive to the growth of hail particles. Hail particles are mainly transformed from cloud water, supercooled rain water and snow particles and then continue to grow by collisioncoalescing with supercooled cloud water, ice crystals and snow particles.