In this paper,the numerical simulation and the diagnostic ananlysis of the structure and characteristic of spiral rain bands around the typhoon "Haitang" during the period of 19th to 20th July 2005 is carried out by using the WRF meso-scale model.The results are as follows.The coastal rain caused by this typhoon corresponds with the activity of the principal and secondary rain bands.The principal band caused by vortex Rossby waves is related well to the 850hPa positive vorticity band and has heavy rainfall.Its low level convergence lies in somewhere of the maximum gradient of temperature and azimuthal winds,however the convergence level of the secondary band is higher than the former.Its maximum gradients of temperature and equivalent potential temperature θ_e occur above 700hPa level without the coordination of the distinct gradient of azimuthal winds.It mainly corresponds with the ladder-shape frontal zone of θ_e near the center of the typhoon.The mergence of the two rain bands brings the strengthening of rainfall.During the period of the landing of Haitang,there exists the break of spiral rain bands.The divergence fields in the middle-low levels west and northwest of the typhoon center result in the strengthening of cyclonic streamline at higher levels.The cyclonic streamline at the high levels and the cyclonic flow of the low-pressure to the west of the typhoon merge into one,producing the mass convergence in this area,which splits the spiral rain bands.When the low pressure at higher levels produces the obvious cyclonic shear,which may also breaks down the spiral rain bands in the down-stream.