In order to further clarify the macrophysical process and hail formation mechanism of hailstorm in southwest China, this study uses the X-band dual polarization weather radar data, ADTD lightning positioning system monitoring data and ground hail observation data, combined with fuzzy logic algorithm and coupling WRF-Elec mode of the NSSL double parameter scheme, analyzes the thermal power, microphysics and lightning activity characteristics of the typical hail monomer on March 13, 2018. The results show that: (1) The development and maturity stage is a key stage in hailstorm process. The graupel particles continue to be generated by the collision of liquid drops with ice crystals and snow with liquid drops, while hail is formed by the collisions of liquid drops with low-density graupel in the “accumulation zone”, and increases by the accretion of liquid water. (2) The occurrence stage of positive ground flash corresponds to the rapid increase stage of updraft location, hail content and ground flash. The anti-tripolar charge structure is the main reason for the dominance of positive ground flash in the hailstorm process. The anti-tripolar charge structure is mainly generated by the convective electric mechanism, which induces a weak negative charge region in the upper part of the cloud, and the duration is short. (3) The strong updraft during the hailstorm played a major role in the growth of the hail embryo, hail formation and the formation of the reverse polar structure. The evolution characteristics of the reverse polar charge structure and the lightning activity characteristics of the hailstorm can be reproduced by using the numerical model. (4) The combination of observation results and numerical simulation is conducive to understanding the thermal dynamic process, microphysical process, the formation of reverse polar charge structure and its relationship with lightning activity characteristics in hailstorm, which has certain guiding significance for the hailstorms prediction in the complex terrain areas of southwest China.