Using the conventional observation data, NCEP (1°×1° lat/lon, 6 hours) reanalysis data and surface intensive automatic meteorological observation data, a severe hail event occurred on 15 May 2010 in Shaya County, Xingjiang is analyzed. The results show that the major influencing systems of the hail event include the low trough over Lake Balkhash and the mesoscale shear line upstream of the hail region, whose vapor came from the west and middle regions of the Tarim basin, gathered and dispersed at the lower levels of the atmosphere. The convergent ascending motion over the hail region provided the vapor and dynamic conditions for the hail. The severe hail event appeared near the high energy region at surface. There existed unstable energies both at the lower levels and in the whole atmosphere before the hail. During the course of the severe hail, there was a mesoscale low pressure, a mesoscale convergence line, and a mesoscale vortex at surface. The severe hail was produced by a γ mesoscale convective cell. The mesoscale convergence line and mesoscale vortex lasted for 5 hours and 3 hours, respectively, and the lifetime of the γ mesoscale convective cell was about 30 minutes.