After analyzing the macro-scale circulation characteristics favourable to the storm rainfall in the Nenjiang-Songhuajiang River basin during 1998 flood period,It′s found that the East Asia blocking high is persistently strong and has a westward position.A longwave pressure ridge maintains between Ural and West Siberian region,and the West Pacific subtropical high and the East Asia blocking high superimpose each other in 130°E.The stable northeast cold vortex is a main reason leading to the storm rainfall in the Nenjiang river and the Songhuajiang river basin in 1998 summer.