In order to study the influence of Doppler radar radial velocity assimilation on the numerical simulation of heavy rainfall， the roles played by WRF and WRF3DVAR in improving the initial fields and simulation results are analyzed.A investigation is conducted on a heavy rainfall event occurred in Guangdong Province on 6 June 2008， and the results indicate that radial velocity， which can be assimilated effectively by WRF3DVAR， affected the initial dynamical field. By adjusting horizontal wind and vertical velocity around the radar station，the mesoscale characteristics of the initial wind field are improved.Moreover， for rainfall simulation， the radial velocity assimilation experiment is better than those without assimilation.