A rain storm associated with a flashflood event is simulated by the Advanced Weather Research and Forecasting(WRFARW) model of National Center for Atmospheric Research(NCAR) and Gridpoint Statistical Interpolation(GSI) data assimilation system of U.S.NOAA.The event is based on a flashflood that occurred in the central Guangdong Province of southeast China during 20—21 June 2005.Comparing to a mixed rain gauge and satellite retrieved precipitation data,the model shows a capability to reproduce the intensity and location of rainfall.However,the simulation depends to a large extent on three conditions:model resolution,physical processes schemes and initial condition.In this case,the Eta Ferrier microphysics scheme and the initialization with satellite radiance data assimilation with fine 4 km resolution nested grid and coarse 12 km resolution outer grid are the appropriate options.