Abstract: very heavy rainstorms that caused severe floods in Pearl River drainage basin from 1949 to 1994 are analyzed here, and it is found that the very heavy rainstorms in Pearl River drainage basin can be divided into three kinds,and they have different characteristics in circulation and physical quantities. Rainstorms that cause floods in Xijiang River and Beijiang River usually happen during the first flood season of the year(Apr.-Jun.). The rainstorms last long, cover large fields and make severe disasters. There are stable circulation background and complete front precipitation systems, and large stratification instability fields. Rainstorms often cause floods in coastal rivers and small tributaries always happen during the second flood season(Jul.-Sept.). They happen suddenly, last a short time but have strong rainfall intensity. They are always caused by tropical cyclones but show significant instability only in rainstorm fields. The characteristics of rainstorms causing floods in Dongjiang River or other main tributaries are like both the above two. That is, they may be connected with fronts or tropical cyclones, and the stability degrees of them are between the above two kinds.