In this study, a hailstorm that occurred in southwest of Guizhou Province on 30 March 2014 is simulated using the mesoscale model WRF (Weather Research and Forecasting). Combined with NCEP/FNL reanalysis data, ground, sounding, Doppler radar data, satellite products and other observation data, this hailstorm process is comprehensively analyzed. In addition, the characteristics of the hailstorm and its environmental conditions, the evolution characteristics of the hailstorm and the characteristics of the cloud microphysical structure, the cloud physical mechanism of the hailstorm are analyzed. The results show that this hailstorm was a typical lowpressure convergence line hailstorm, and the hail position on surface was at (or southern to) shear line at 700 hPa, closing to the ground convergence line. The convective cloud of this process underwent the initial stage, the consolidation stage, the maturehail stage and the eastward shift stage. Thus, the microphysical structure of convective cloud over Guizhou Province has the characteristics of mixed phase cloud with ice crystal and snow in upper layer, cloudwater and graupel in midlayer, and rainwater and hail in lower layer. The most important sources for the rainwater and hail are the graupel and cloudwater. During the process of hail formation, the accretion between graupel and supercooled cloudwater, and the automatic conversion of graupel are the main microphysical mechanism.