Analysis on the storm rainfall in Wuhan from 08:00 to 14:00 on July 22,1998 illustrates that the process,with the background of an ascending branch of subtropical meridional circulation,is independent of south warm area and north cold air.Low inflow air and high outflow air play an important part in the forming and maintaining of the large scale rain region.The heavy rain is directly resulted from up and low coupling of boundary layer southerly jet,low westerly jet and high westerly jet.Southerly jet at 925hPa is the chief provider of water vapor and trigger of convective instability energy release;moreover,low westerly jet at 850hPa contributes much to the forming and maintaining of convective instability at middle and low level,while mid latitude high westerly jet to the forming and maintaining of symmetrical instability at high level.The storm comes into being owing to coupling of the three jets which develop and strengthen the convective and ascending air movement at mid low level.