A dynamical analysis of two torrential rainfall events in June 2005 in Guangzhou is made with the routine meteorological data, automatic weather station data, NCEP reanalysis data and numerical model outputs. The similarities and differences between two torrential rains are found from aspects of environmental conditions and physical mechanisms. It is found that (1) the cold air from east is likely the trigger mechanism of the torrential rain on 5 June; (2) the pulse of the jet in the southwest monsoon flow and the surface mesoscale low pressure may be the trigger mechanisms of the torrential rain on 21 June.