Using NCEP (1°×1°) 6 h reanalysis data, observational data and new generation Cband Doppler radar data, a strong thunderstorm process in Keping, Aksu in August 19, 2009 was investigated. The results show that the mesoβ shear line, the surface mesoscale low and the convergence line are the direct affecting systems of thunderstorm. The water vapor came from the eastern and middle regions of Tarim Basin, and the water vapor transportation was concentrated at low levels, where the easterly jet stream took a vital part in the water vapor transportation. Convective available potential energy had increased before the thunderstorm occurred. The thunderstorm developed initially from an ordinary rainstorm, then evolved gradually into a hailstorm, and lasted more than an hour. The reflectivity of the hailstorm at its mature stage displayed a middlelevel echo overhang aloft and weakecho region.