On 21 March 2019, a large-scale convective weather disaster occurred in the southern part of the south to Yangtze River, and it was also the first regional severe convection case encountered after the dual-polarization transformation of the Ji’an SC Doppler Radar in southern Jiangxi. Based on the radar detection data, the distribution and evolution characteristics of the dual-polarized radar parameters were analyzed, and compared with the observation data of cloud-to-ground flashes (CGs). Besides, the differences in performance characteristics between short-time severe rain and hailstorm were explored. The results show that in this case the increase of the horizontal reflectivity ZH and the differential reflectivity ZDR at low elevation angles are significantly ahead of the change of ground rainfall, while the changes of CGs frequency are more advanced, over 6 min earlier than ZH and about 5-10 min earlier than ZDR. The peak time of KDP lags behind lightning for about 15 min, which could help to predict the evolution trend of ground rain intensity in this process. During the hailstrom process, the moment when ZH begins to increase is about 15 min before the ground sag, and the other polarizations advance even earlier. At the same time, CGs increase rapidly when hail occurs. These characteristics have a good indication for hail predictions in this process. In addition, this paper also explores the relationship between the precipitation value M of ice particles and hail. It was found that it surges 15 min ahead of falling to the ground, and the higher the altitude, the earlier the M peak appears. This could provide reference for predicting the possibility moment of hail.