Based on the synoptic analysis for a heavy rain event occurred in Shanxi on 1—2 July 2005,using the new generation mesoscale model of Weather Research and Forecasting(WRF) with two-way nested grid,the numerical simulation of the rain event is performed in this paper,and high spatial and temporal resolution model outputs are used to diagnose the relation between removal entropy index and rainfall area.Diagnostic results show that the event is caused by active subtropical high;the rainfall area matches well with the mid-low level convergence and the upper-level divergence,and the the SW low-level jets provide vapor and motive terms and play an important role in the heavy rain event.Results also show that the negative entropy change(I_RE<0) area corresponds to the large-scale heavy rain area;the convergence of the negative entropy change indicates the location of heavy rain;and the removal entropy index match the heavy rainfall centers quite well.