A detailed analysis on the evolution of stream fields and echo structures of a supercell hailstorm that occurred on April 17, 2011, is conducted on the basis of Doppler radar data combined with radio sounding and surface observation. The main results are as follows: The hailstorm occurred in a conditional instability and significant vertical wind-shear environment, which belong to right-moving storms. A cross-section of the development stage shows that an organized updraft was formed gradually, which promoted the formation and development of the hail cloud. During the hail-forming stage, a strong, tilted updraft and deep mesocyclone manifested in the hailstorm; the main updraft corresponded to the weak echo region. The hailstorm maintained a typical bounded weak echo region (BWER)- overhang-echo-wall-echo structure. According to the evolution of zero velocity line, which connects the radar radial velocity and the speed of hailstorm, the line approached the overhang echo zone with hail cloud development and crossed the overhang echo. The trend of zero velocity line was upturned, and the collection power of the cave channel near the line was sufficiently strong to form hail. The hail formation area can be analyzed through the determination of the zero velocity line. A method of identifying the characteristic structure of the hail-forming region is also presented in this study. According to the strong echo dislocation of high and low levels, the characteristic structure is determined quickly and accurately from the strong echo center section at two heights. Moreover, a 45 dBZ region at a 6 km height above the 0℃ layer is identified as the hail-forming region, where the potential of hail is calculated to be 100%.The identified hail region is in contrast to the actual hail observation.