Numerical simulation of a Mei-yu front storm rainfall which occurred in Jiang-huai area on July 4~6,2003 was given,using the new generation fine grid mesoscale numerical model named WRF and the MM5(V3) numerical model respectively. Results indicate that WRF and MM5 both can imitate distribution and tendency of the rain belt of this storm rainfall course. And WRF can imitate the location and amount of the precipitation center better. Furthermore,WRF's simulating result of distributing character of circulation pattern,low-level-jet and eddy field are better than MM5's.Contrasting with the dynamical frame of the two model,MM5 simulates an illusive circulation at east of Yun-gui tableland which ought to have relation to the difference of the vertical coordinate of the two models. Analyzing WRF's simulating result，we find that the area with negative 700 hPa moisture potential vorticity is well corresponding with rainstorm area.