The heavy rainfall in Changde on 13 May 2002, Hunan Province in 2002 was analyz ed based on Doppler weather radar products, NCEP 1°× 1° reanalysis data, satellite cloud image products, realtime detection data and MM5 numerical simulations. It is found that the rainfall event was caused by joint influences of upperlevel troughs, middlelowlevel shears, southwest jets, ground inverted troughs and a weak cold air. How the jet formed, developed and weakened had a direct impact on the intensity of rainfall. The rainfall center corresponded well to the “U"shaped gap of satellite cloud image and the middlelow jet axis of Doppler base velocity field. When the jet in the Doppler basic velocity field vibra ted, the cold advection above the low level warm advection appeared, lowlayer cyclone vortex field formed and maintained, and l owlevel vertical wind shear changed, it could instruct conspicuously that heavy rainfall would occur. Numerical simulation has proved the mesoscale vortex, jets and convergence to be consistent with those detected by radar. All these results have valuable reference to rainfall nowcasting.