Abstract: In summer of 1991 heavy rainfall and flood took place over the wide regions of China and made much loss of life and property. The analysis on the cause of this storm rainfall was made with the ECMWF grid wind and other routine data. The results point out that the anomalous strength and the channel's change of the cross-equatorial flow(CEF) during May to July 1991 are one of the main reasons producing this heavy rainfall.At the sametime,the earlier outbreak of cold air over the middle-high latitude of the Southern Hemisphere may be a:signal of the 1991's abnormal CEF.