By forecasting and diagnosis of extraordinary rainstorm in the lower-middle reaches of Changjiang River on July 22 ,1998 and July 4, 1983, it is shown that the upper cold-air piling up left of lower jet is the main structure fe ature, diagnosis of physical parameters and its tendency shows that there are re lations between heavy precipitation or severe convection area and strong conver gence area at 850hPa to 500hPa level and strong convergence area of vapor flux in future. The rain area can be better estimated by computing the tendency than the physical parameters.