Abstract:The activity of cold air during the torrential rain at 18~26th June,1998 in South China(SC)is analyzed by using the potential vorticity(PV)theory.Results show that under the situation of persistent East Asian(EA)blocking pattern,the southward air from midand high- latitude rushed into the area between South of the Yangtze River and SC three times,corresponding to three times of heavy rain.The air was cut by the Southwest and Southeast warm-moist air flow from low latitude in the vicinity of South of the Yangtze River,and formed a high PV center of cold air.As the result of the interaction of cold and warm airs,the EA temperature field displayed a particular pattern,i.e.,a low center accompanied by two high areas in South and North respectively.