Abstract:The torrential rain brought about by a South west China vortex in Changjiang Gorges and its vicinity in 28—29,June 1998 was simulated using MM5.Comparing the two simulations with different model topography schemes,it is indicated that the mountains in east Sichuan Basin has no significant effects on the genesis of South west China vortex,but has important influence on the intensity and the feature of distribution of the heavy rain events.Mainly,the warm and wet flow was blocked by Daba-Shenonggia mountain range and resulted in a torrential rain bend to the windward foot of the mountain range,which was also a heavy rain region at the windward slope of the southwest Hubei mountainous district,and the east moving precipitation system was detained by the mountains in east of the basin,as the sequence,the precipitation strengthened upstream and weakened downstream.