Abstract: The heavy rainfall IOP case of the HUAMEX project during 23—24 May 1998 is simulated by using the non-hydrostatic meso-scale model MM5 (V2). Results show that the cold cloud process in which ice phase is coexisted with super-cooled liquid phase of cloud water plays the most important role in the formation and development of convective heavy rainfall in South China. The warm process (condensation and aggregation of liquid droplets) for the formation and development of rains in South China may play a role only for the non-convective precipitation with larger scale but not very strong intensity.