Using the new generation mesoscale model of Weather Research and Forecast(WRF),with the high resolution grid points and the suitable physical schemes,the numerical simulation of the rain gush of the Jianghuai Meiyu front during 4th-5th July 2003 is carried out.Simulated results show that the rain gush and the genesis and development of the mesoscale system are well described,and the distribution,intensity and center location of the precipitation are successfully forecasted.The low-level jet,slantwise instability development,and the mesoscale low vortex system and the perturbation in the upper troposphere are analyzed,and it is found from the simulated results that the development of tilted vertical vorticity is the dynamical mechanism for the genesis and development of the low-level vortex.The sufficient moist available potential energy and latent heat release offer the material condition for this heavy rain event.