By analyzing the change of moist potential vorticity (mpv) field and baroclinicity, a heavy rain event occurred in the northeast Huaihe basin from 30 to 31 August 2000 is discussed. It is found that this heavy rain is closely related to the typhoon disturbance which triggered off the evolution of circulation field. Furthermore, the key of the heavy rainfall is interaction between the typhoon warm and wet weather system and the cold convergence system.