Abstract:The dual characteristics of its topography and urban boundary layer in Beijing area result in weather change diversity. The effects of s uch underlying surface physical process on the strong convective weather evoluti on are analyzed by combining a severe hail event occurred on May 31 2005 in Beij ing. Results indicate that the mountainous topography and urban boundary layer h ave great effects on the hailstorm evolvement, even on the hail falling area and intensity. The initial radar echoes of this case are sprung locally by the ther modynamic circulation and dynamical forcing induced by the mountainous topograph y in the west. The primary factors that intensify the convective radar echoes wh en it moves over the centre city downtown include the surfacemesoscale wind fie ld convergence line engendered by urban underlying surface thermodynamics effect s, as well as the air ascending and the congregating energy and water vapor. Als o, the trumpet like topography in the north mountainous area and the windward s lope uplifting in the west have significant influence on the occurrence of local strong convective process and the development of those moving in cumulus.