The reason of the extreme rainfall event occurred in 3-5 August 1996 over Hebei province has been studied using conventional meteorological data and satellite imagery.The results show that the event presented itself in a strong meridional circulation in eastern Asia and stronger lowlevel southern jet which was caused by stronger pressure gradient between typhoon low and subtropical high.The jet transmitted high thermal and moisture air from the tropics to North China,and interacted with weaker cold air near surface.And generated and developed were two mesoscale cloud clusters causing the extreme rainfall directly.