To further explore the formation and development of hail cloud in Guizhou Region and the transformation mechanism of microphysical conditions during the growing process of hail, 12 hail cases during 2012-2015 are studied through numerical simulation using threedimensional hail cloud model. The results show that: all kinds of water into the spatial distribution of hail is the material basis of the hail growth, and rising air and water vapor phase change with a positive feedback effect. The hail particles grow mainly taking graupel particles as embryo, and growth mode is given priority to sleet automatic conversion. In the process of continuous development of hail, hail cloud at the end of the first developing process, there is still 0℃ layer with 4 km or lower thickness which is the thermal environmental condition for the development of hail cloud again. In the hail area the surface airflow are divergent, leading to the formation of stronger updraft convergence on both sides, which is dynamic conditions for the development of hail cloud again. At the same time, the air convergence makes the water vapor the original hail air continuously flow into the air convergence zone on both sides, which becomes water vapor source of the hail cloud development. The rapid increase of ice crystals and graupel particles in the hail cloud provides favorable microphysical material conditions for the growth of hail again.