A heavy rain occurred in the middle reach of the Yangtze River during 22~23 July 2002 is simulated using AREM model.The simulation results indicate that the distribution of precipitation zone simulated is very similar with the actual precipitation.A serial of meso-β-scale vortexes and depressions are simulated in this process.The analyzed results shows that the development of the low level jet is the most important cause to produce these changes.The moving upwards and northwards of the axis of low level jet enhances the gradient and shear of the wind which is located in north of the jet,bringing acute change of the vorticity.The development of positive vorticity leads to the genesis of meso-β-scale system at last,which order is from low to high levels.The track of the simulated rain group approach to the track of meso-β-scale low pressure.