By using the conventional meteorological data，a meteorological analysis on the large scale circulation background，the synoptic scale influencing systems，the hourly evolvement of satellite cloud image and the atmospheric stratification stability that caused the formation and the development of the meso - α - scale convective system，which caused the severe convective weather process on May 30，2005，was done in this paper；and based on the physical quantity products of T213 numerical weather forecast model，a dynamic analysis on the distribution of physical quantity fields of the system was also done. The results show that under the favorable conditions of temperature and humidity and dynamic factors，such as the Mongolia cold vortex rotating and moving eastwards and southwards，the existence of both the high - level and low - level jet stream，the warm and wet tongue extending in the low layer，the cold and dry tongue in the middle layer，and the large area convective instability，several meso - γ - scale convective systems were excited，then they united into several meso - β - scale convective systems，eventually，the meso - α - scale convective system was formed by the coalition of the several meso - β - scale convective systems.
