Using the Doppler weather radar data, combined with the sounding data and precipitation data, the mean radial velocity and ultra-low-level jet characteristics of four torrential rain processes were analyzed. The results show that four torrential rain processes had higher K value, smaller temperature difference between 850 hPa and 500 hPa, abundant water vapor and weaker vertical wind shear in middle and lower layers. Similar flow field structure in low-level and “S” type zero radial velocity contour of four torrential rain processes indicated that warm air advection was occurring.30 mm or more hourly rainfall occurred when the ultra-low-level wind speed (from radar VWP products) reached 10 m〖DK〗·s-1 or above and wind speed difference between upstream and downstream radar exceeded 5 m〖DK〗·s-1.The ultra-low-level wind speed reached 12 m〖DK〗·s-1 or more and wind speed difference between upstream and downstream radar exceeded 15 m〖DK〗·s-1, the precipitation intensity furtherly strengthened and maintained. The establishment and maintenance of the ultra-low-level jet,and the ultra-low-altitude convergence between the upstream and downstream radar provide the energy, water vapor and dynamic conditions for the development and maintenance of the precipitation storm, and play an important role in the formation and persistence of the heavy rainfall.