Abstract:Based on the conventional observation data,radar reflectivity data and FNL reanalysis data from NCEP/NCAR, and combined with the simulation results by non-hydrostatic mesoscale model, the environment background, moving path, intensity difference and its causes of the short-term strong rainfall and hail in two squall line processes during June 3 to 6,2009 were analyzed. Results indicate that the different steering flows below 500 hPa lead to the different moving paths. Numerical simulation and water vapor test show that the main reason why the intensity difference of short-term precipitation and hailstone occurred on June 3 and June 5 is the differences of water vapor in vertical structure. The water vapor content at 700-850 hPa is very sensitive to graupel(hail). When the water vapor in this area increases, the water proportation in graupel(hail) increases significantly, otherwise, it significantly reduces.