With the TBB data from FY-2C satellite and the hourly observed precip itation data，the TBB features of torrential rain causing flood in Sout h China from 18 to 22 June,2005 are studied．The results show that TBB can direc tly and quantitatively present the features of the intensity and distribution of the cloud sys tem with heavy rainfall. The torrential rainfall area is basically in the lower TBB band. The rainfall intensity increases when TBB decrease s. The daily variation of the rainfall intensity is in accord with that of TBB．The strong southwest monsoon plays a key role in the development and enhancement of the strong conve ctive cloud cluster in South China.