Using the data of the wind profile delivered every six minutes by the new genera tion of weather radar of Yingkou，the detailed analysis is made for the lowlev el wind field structure duringthe heavy rain periods of torrential rains on 29 June 2006 in the w est of Liaoning Province. The conclusion is as follows: The incidence of the heavy rain is corresponding to the rapid strengthening of l owlevel jet and its downward expansion. The southwest lowlevel jet in advan ce of two hours before the shortterm heavy rain starts to move downward rapidl y . The fluctuation in the low level and its degree of expansion towards the grou nd has a close relation to the strong shortterm rainfall. The lowlevel jet w ill not certainly immediately cause a strong rainfall when it arrives at the sta tion，sometimes this process will be delayed one or two hours. The emergence of the strong rainfall or the strong weather has definite momentum transmission. It strengthens the lowlevel disturbance and the strength of lowlevel jet. The extended height and the magnitude of the momentum transmission restrict directly the strength of the strong rainfall. The degree of increase in the lowlevel j et index (I) and the intensity of rainfall has a direct proportional relationsh ip. Index (I) not only indicates that the fluctuation of lowlevel jet and the intensity of ground expansion have a close relationship with the strong rainfall of meso scale，but also indicates the occurrence of strong rainfall a nd the magnitude of rainfall intensity.