Two heavy rain cases are simulated with the PSU/NCAR mesocale model.For control experiments,both the surface and upper air observation are used in the initial fields.For sensitive experiments,the initial fields are the same with the control ones,but the real time GMS satellite convective cloud cluster data are used to modify the initial moisture fields.The results show that (1)because the convective cloud data strengthen local moisture fields,both the convergence and updrafts of the low-middle troposphere over the heavy rain center and its peripherial areas intensify and reach maximum in strength about fourth hour in sensitive experiments;(2)because of the use of convective cloud data,the simulated rainfall in the first 4～6 hours is greater than that in the control experiment,and it is closer to the real rainfall;(3)if the modified initial moisture field is initialized with the other initial fields,then the duration of humidity effect is greatly extended.