Abstract: In order to explore the evolution characteristics of interactions between thunderstorm monomers during hailstorm, by using X-band dual linear polarization weather radar data, two-dimensional lightning monitoring data and the combination of conventional meteorological sounding and ERA5 reanalysis data, the merging characteristics of thunderstorm monomers during a hailstorm on 30 April 2018 in Weining County, Guizhou Province are analyzed. The results show that: The hailstorm was mainly affected by the merger of the two monomers, with the occurrence of “Cloud Bridge” at the beginning of the merger, and the heavy precipitation of the two monomers in the early stage of the merger promoted the growth of the joint. The merger strengthened the overall development of the convective system, and the interaction of updraft and downdraft airflows in the early stage of the merger reduced the peak height of thunderstorm echoes. The hail particles showed an increasing trend in the merger stage, and the maximum value of hail particles mainly occurred 6 minutes before the end of the merger and 6 minutes after the merger. In this weather process, the number of negative cloud-to-ground flashes accounted for 94% of the total cloud-to-ground flashes. The frequency of lightning jumped and peaked during the merger stage, and the larger rising speed made the growth rate of low-density graupel particles and ice crystal particles exceed 5 times that of high-density graupel particles, while the non-inductive collision between low-density graupel particles and ice crystal particles was the main electrification process. After the merger, the echo peak dropped, the updraft airflow weakened, and the large particles fell. Affected by the nearby newborn convection, the graupel particles and ice crystal particles in the system increased in a short time, and the frequency of lightning increased again.