The influence of the change of the upper level westerly jet on the precipitation intensity and the position of rain band of a torrential rain process in the middle lower reaches of the Yangtze river is investigated in this paper using the MM5 (V2).Numerical experiment results show that the control experiment (CTL) is able to successfully simulate the position of the upper/low level jet and the intensity of precipitation;in the sensitive experiment,the technique used to strengthen/weaken the upper level westerly jet (SJet/WJet) is reasonable as well as feasible.The influencing processes of SJet and WJet on the low level circulation and the precipitation intensity of rain band are different;SJet is favorable to the strengthening of the low level jet,thus leading to the increase of precipitation south of and the reduction north of the rain band in the CTL,this corresponds to the circumstance of the withdrawal of the rain band;while WJet is favorable to the northward advance of the rain band.Therefore,SJet results in the position of torrential rain center south than normal,and WJet leads to the position north than normal.