Abstract: The charact eristics of the mesoscale convective systems of a torrential rain case occurring over south Yangtz River on 16-17 June 1998 are invest igated by using mesoscale numerical simulations and observations as well as 1998 field-experiments data. It has been revealed that the torrential rain occurs associated with the generation of a mesoscale convergence line in the region to the south of a mesoscale low in lower-troposphere; under the weak vertical wind-shear condition, several meso-β clouds, the convect ive systems directly relat ed to the torrential rain, develop st rongly in vertical like towers within a meso-β cloud; and before the occurrence (about 8 h) of the torrential rain, the maximum value of convection available potential energy could reach 2600 J/kg, which is gained through the intensive sounding data from 1998 field experiments.