The torrential rain from 4 to 5 August,1996 in Beijing area is the result of interaction among typhoon low,subtropical high and shear line.Before torrential rain,the tongue of high energy stretched from Central China to North China,and the energy in Beijing area increased rapidly.In torrential rain area,not only did the southerly low level jet transport water vapour and energy to it,but also did the wind velocity fluctuation of the jet trigger the release of moist available potential energy.