By using mesoscale NWP model (MM5)，the rainstorm process occurred in the east of Fujian is numerically simulated.The fine resolution results of model output is used to diagnostically analyze some physical variables.It is shown that the mesoscale low-vortex is one of the dominant systems in the process and its characteristics on temporal and spatial variation is coincident with that of center of precipitation.The experiment on the wind field indicates that upper and lower jets provide abundant moisture for the rainstorm，and they are also one of the trigger mechanism of the rainstorm.