Abstract: Herein, the WRF model was used to simulate the hailstorm in Beijing on June 25, 2021. In terms of radar reflectance and precipitation, numerical simulations reproduce the macroscopic characteristics of a hailstorm. Based on this, the mesoscale thermal, dynamic, and microphysical characteristics of a hailstorm in various development phases are examined. Finally, the mass budget and latent heat budget of hail particles and raindrops are studied by outputting the intermediate transformation term of the microphysical process, and a conceptual model diagram of the cloud microphysics of hail formation is presented. The results reveal that the process of hailstorm can be divided into three phases: multicell echo, linear convection, and squall line. In this hail weather, snow particles are primarily hail embryos, forming hail particles by the accretion of rain and cloud water by snow in the middle and upper troposphere; thereafter, the hail particles grow through the accretion of rain and cloud water by hail. The production rate for rain accretion by cloud ice or the accretion of cloud ice by rain to form hail particles is very low. The airflow flows at the front lower level of the storm, and the two weak updrafts of the multicell phase constantly combine. In the linear convection and squall line phases, the inflow of the low layer is weakened, while that of dry and cold air is evident in the middle and high layers. The air flow strongly increases in the squall line phase and flows forward at the upper level. The warm and humid air lifted by the updrafts meets with the dry and cold air flowing in from the middle and upper layers and condenses into cloud water or ice-phase particles, releasing a large amount of latent heat, which leads to the enhancement of the buoyancy force inside the clouds and promotes the strong rise of the airflow inside the clouds, and more cloud water and ice-phase particles will be generated. The melting of snow and hail particles absorbs large amounts of latent heat, causing the melting layer to rise. Therefore, a large amount of supercooled rain forms in the squall line phase, increasing the production rate for rain accretion by snow to form more hail particles. The low-level downdraft is enhanced by the strong drag of the water material caused by the fall of large hail particles. Downdraft causes evaporation of rainwater at lower levels, forming cold pools near the surface by the cooling effect, which enhances convection with latent heat heating at higher levels. Therefore, it positively feeds back to the meridional circulation. The vertical updraft resulting from the circulation promotes the water vapor in the lower layers to rise above the melting layer and condense into supercooled water and snow particles, while the vertical downdraft promotes snow and hail to melt into rainwater and evaporate below the melting layer and then positively feeds back to the thermal environment within the cloud. This repetition produces hail and heavy precipitation.